ANATOMY OF THE SPINAL CORD. Structure of the spinal cord Tracts of the spinal cord Spinal cord syndromes

Transcription

1 SPINAL CORD

2 ANATOMY OF THE SPINAL CORD Structure of the spinal cord Tracts of the spinal cord Spinal cord syndromes

3 The Nervous System Coordinates the activity of muscles, organs, senses, and actions Made up of nervous tissue Has 3 main functions: 1. Receives sensory Input 2. Integration 3. Dictates motor output

4 Spinal Cord

5 Spinal Cord Functions Pathways for nerve impulses within tracts Ascending (sensory). Example: spinothalamic Descending (motor). Example: corticospinal Reflexes: fast, involuntary sequences of actions in response to stimuli Can be simple (withdrawal) or complex (learned sequence such as driving car) Levels Spinal (reflex arc): simple Cranial: more complex Copyright 2010, John Wiley & Sons, Inc.

6 Reflex Arc 1. Sensory receptor: responds to stimulus 2. Sensory neuron: through dorsal root ganglion and root posterior horn 3. Integrating center: single synapse between sensory and motor neurons 4. Motor neuron: from anterior horn ventral root spinal nerve 5. Effector: muscle responds

7 Example of Reflex Arc: Patellar Reflex 1. Sensory receptor is stimulated by tap on patellar tendon 2. Sensory neuron: through dorsal root spinal cord 3. Integrating center: single synapse in spinal cord 4. Motor neuron: through ventral root spinal nerve femoral nerve 5. Effector: quads contract, extend leg

8 Example of Reflex Arc: Patellar Reflex

9 General Organization Spinal cord is SMALL! cm long 1 CM wide at widest point Does not extend all the way to the bottom of the spinal column Pattern of grey/white matter is reversed in the cord White matter tracts on outside Grey matter on the inside Staining reverses this!!!

10 General Organization White matter (tracts of axons) axons) Grey Matter (cell bodies) )

11 General Organization Spinal cord is segmented anatomically Input and output occurs in groups of rootlets arranged in a series longitudinally along the cord Dorsal rootlets -- Input -- carry sensory information Ventral rootlets -- Output -- motor neurons

12 General Organization Each set of rootlets forms a spinal nerve that innervates a corresponding segment of the body, called a dermatome

13 General Organization

14 General Organization There are 31 segments in the spinal cord: 8 cervical (C1 - C8) 12 Thoracic (T1 - T12) 5 Lumbar (L1 - L5) 5 Sacral (S1 - S5) 1 Coccygeal

15 General Organization The spinal cord is housed within the vertebral column

16 General Organization Each cord segment has a corresponding vertebra of the same name (e.g., C3) Spinal nerves enter/exit underneath their corresponding vertebral segment

17 General Organization

18 Grey and White Matter

19 Grey and White Matter Grey Matter = Cell Body White Matter = Myelinated axon

20 Grey and White Matter Grey matter Cortex Nucleus (CNS) Ganglion (PNS) Exception: Basal Ganglia

21 Grey and White Matter White Matter Nerve (PNS) Tract (CNS) Fasciculus/Funiculus -- Group of fibers with common origin and destination Lemniscus -- Ribbon-like fiber tract Peduncle -- Massive group of fibers -- usually several tracts

22 Grey and White Matter Tracts are named with origin first, then destination Corticospinal tract -- cortex to spinal cord Mammilothalamic tract -- Mammilary bodies to thalamus Spinocerebellar tract -- Spinal cord to cerebellum Corticobulbar tract -- Cortex to brain stem

23 DIVISIONS OF THE NERVOUS SYSTEM Central Nervous System (CNS) Brain and spinal cord Interprets incoming sensory signals Dictates motor responses Peripheral Nervous System (PNS) Ganglia Nerves Cranial nerves and spinal nerves Communication between regions of body and CNS

24 Spinal Cord - Spinal Nerve (C8, T12, L5, S5, Cx1) - Segmental Structure of Neural Tube Origin - Comparable to Input-Output (IO) System of the Computer

25 Spinal cord

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28 Spinal cord Internal gray matter: presence of neurons relaying and integrating motor/sensory impulses Fiber tracts: sensory and motor

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30 Spinal cord Segmental organization derived from neural tube and somites Spinal segments - 31 Spinal nerves: C8, T12, L5, S5, Co1 Comparable to input-output systemof computer Seat of reflexes Origin of ascending and descending projections

31 Somatic PNS ANS Sympathetic Parasymp. Enteric CNS

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33 PNS Nervous system structures outside the brain and spinal cord Structural components: Sensory receptors Motor endings Nerves and ganglia

34 PNS - Nervous Tissue Made up of 2 cells: Neurons Conduct nervous impulses Supporting cells Surround the neurons Ex. Glial cells

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36 The Neuron Nerve cells Transmit signals in form of nerve impulses Have extreme longevity Do not divide High metabolic rate

37 Neuron-To-Neuron Transmission synapses

38 Neuronal Anatomy Cell body (soma) Most are in CNS Neuron processes Dendrites Toward cell body Axons Transmit away from cell body Synapses Site where neurons communicate

39 Neuronal Anatomy Myelin sheath Fatty sheath that surrounds most nerve fibers Reflex arc Responses to a stimulus Interneuron Nerve cell that lies between a sensory neuron and motor neuron in a reflex arc Confined entirely within the CNS

40 PNS - Sensory and Motor Signals Divided by the body regions they serve: Sensory division Somatic sensory Visceral sensory Motor division Somatic motor Visceral motor

41 The Spinal Cord Foramen magnum to L1 or L2 Runs through the vertebral canal of the vertebral column Functions 1. Sensory and motor innervation of entire body inferior to the head through the spinal nerves 2. Two-way conduction pathway between the body and the brain 3. Major center for reflexes

42 Spinal cord Fetal 3 rd month: ends at coccyx Birth: ends at L3 Adult position at approx L1-2 during childhood End: conus medullaris This tapers into filum terminale of connective tissue, tethered to coccyx Spinal cord segments are superior to where their corresponding spinal nerves emerge through intervertebral Denticulate ligaments: lateral shelves of pia mater anchoring to dura (meninges: more later)

43 The Spinal Cord white matter dorsal root grey matter pia mater ventral root arachnoid spinal nerves dura mater

44 The Spinal Cord vertebra spinal cord spinal nerve

45 Nerve Pathways into the Spinal Cord sensory pathway motor pathway

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47 Autonomic Nervous System Visceral Motor Function Not easily controlled by will Get nervous and sweat Innervate smooth muscle, cardiac muscle, glands Regulate visceral function Heart rate, blood pressure, digestion, urination Has 2 divisions: Parasympathetic Sympathetic

48 ANS Parasympathetic Enables body to unwind and calm down Most active when body at rest Routine maintenance functions Craniosacral division Fibers emerge from brain and sacral spinal cord Sympathetic fight or flight Mobilizes the body during extreme situations Becomes active when extra metabolic effort needed Thoracolumbar division Fibers arise from thoracic and lumbar parts of spinal cord

49 ANS Includes a chain of 2 motor neurons Preganglionic neuron Preganglionic axon Ganglionic neuron Postganglionic axon Autonomic neuron synapses 2 neurons

50 PNS Somatic NS Autonomic NS Sympathetic division Parasympathetic division Enteric division

51 Somatic Nervous System Innervates skeletal muscle Neurons runs from CNS directly to muscle Consists of single neuron plus skeletal muscle cells Voluntary control Running, moving limbs, typing on a computer!

52 CNS Spinal Cord Runs through vertebral canal of the vertebral column Protected by bone, meninges, and cerebrospinal fluid Spinal cord made of a core of gray matter surrounded by white matter 31 pairs of spinal nerves branch off spinal cord through intervertebral foramen Functions in many ways: Involved in sensory and motor innervation of body inferior to the head (through spinal nerves) Provides a 2-way conduction pathway for signals between body and brain Major center for reflexes

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54 Spinal Cord Growth Until 3 rd month of development, does not run to coccyx As vertebral column grows caudally, spinal cord becomes more rostral At birth, ends at L 3 During childhood, terminates at L 1 and L 2 Adults runs from medulla oblongata to L 1

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56 Regions of the Spinal Cord Cervical Thoracic Lumbar Sacral Coccygeal Cervical + Lumbar enlargements Cauda equina Conus medullaris Filum terminale

57 Protection: Bone Meninges CSF (cerebrospinal fluid) 3 meninges: dura mater (outer) arachnoid mater (middle) pia mater (inner) 3 potential spaces epidural: outside dura subdural: between dura & arachnoid subarachnoid: deep to arachnoid

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59 Spinal Meninges and Spaces Epidural space: between vertebrae and dura mater Dura mater- tough,dense connective tissue Extends to vertebra S2 (well beyond spinal cord) Arachnoid mater: resembles spider s web Extends into subarachnoid space Subarachnoid space CSF circulates in this space Pia mater: thin, delicate layer Adheres to surface spinal cord (and brain) Contains blood vessels Copyright 2010, John Wiley & Sons, Inc.

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61 Spinal Meninges and Spaces Copyright 2010, John Wiley & Sons, Inc.

62 Meninges of Brain and Spinal Cord Dura mater (superficial) Spinal dural sheath Does not attach to bone Epidural space Fat and veins Between dura mater and vertebra Subdural space Between dura mater and arachnoid

63 Meninges of Brain and Spinal Cord Arachnoid mater (middle) Impermeable layer = barrier Raised off pia mater by rootlets Subarachnoid space Between arachnoid and pia mater Contains CSF Pia mater (deep) Highly vascular Adheres to brain/spinal cord tissue

64 Meninges of the spinal cord Dura mater Arachnoid membrane Pia mater Denticulate ligament - specilization of the pia mater - landmark for cordotomy

65 Meninges of the spinal cord

66 Meninges of the spinal cord

67 Gray Mater Consists of neuron cell bodies, unmyelinated axons, dendrites, and neuroglia Shaped like an H Gray commissure (crossbar) Central canal Posterior horns Anterior horns

68 Gray Mater Posterior horns Consist of interneurons that transmit in from outside spinal cord into it Dorsal root contain sensory fibers Somatic Sensory (SS) Visceral Sensory (VS) Dorsal root ganglia - swelling in dorsal root that these interneurons pass through Anterior horns Cell bodies of motor neurons send info out of spinal cord to muscles and glands Ventral Root contains Motor Fibers Visceral Motor Somatic Motor

69 Arc reflex Arc reflex (fast and involuntary)

70 White Mater Surrounds gray matter Composed of myelinated and unmyelinated axons Divided into white columns (funiculi) Posterior funiculus Anterior funiculus Lateral funiculus Allow for communication between Parts of the spinal cord Spinal cord and brain

71 White Mater 3 types of nerve fibers: Ascending Carry sensory info from sensory neurons of body to brain touch, pressure, pain, temperature Descending Carry motor instructions from brain to spinal cord Contraction of muscles and secretion of glands control precise, skilled movement = writing, maintain balance, create movement Commissural Cross from one side of cord to the other

72 Gray and White Matter Like spinal cord but with another layer of gray outside the white Called cortex Cerebrum and cerebellum have Inner gray: brain nuclei (not cell nuclei) Clusters of cell bodies Remember, in PNS clusters of cell bodies were called ganglia More words: brains stem is caudal (toward tail) to the more rostral (noseward) cerebrum

73 Gross Anatomy of Spinal Cord Extends from medulla of brain to L2 vertebra Cauda equina (horse s tail) Extends inferior to end of spinal cord Consists of roots of lumbar, sacral and coccygeal spinal nerves Left and right halves partially separated by Anterior median fissure and posterior median sulcus Small central canal (filled with CSF) in middle Enlargements: cervical and lumbar regions Points of origins of nerves to upper and lower limbs Copyright 2010, John Wiley & Sons, Inc.

74 Gross Anatomy of Spinal Cord Copyright 2010, John Wiley & Sons, Inc.

75 Internal Structure of Spinal Cord Copyright 2010, John Wiley & Sons, Inc.

76 Spinal cord eneral_esi_epidural_space.jpg coverings and spaces Dura mater Arachnoid mater Pia mater

77 Spinal cord anatomy Posterior median sulcus ( p ) Anterior median fissure ( a ) White matter (yellow here) Gray matter (brown here) p a

78 Gray/White in spinal cord Hollow central cavity ( central canal ) Gray matter surrounds cavity White matter surrounds gray matter (white: ascending and descending tracts of axons) H shaped on cross section Dorsal half of H : cell bodies of interneurons Ventral half of H : cell bodies of motor neurons No cortex (as in brain) Dorsal (posterior) white gray Central canal Ventral (anterior)

79 Spinal cord anatomy Gray commissure with central canal Columns of gray running the length of the spinal cord Posterior (dorsal) horns (cell bodies of interneurons) Anterior (ventral) horns (cell bodies of motor neurons) Lateral horns in thoracic and superior lumbar cord * * *

80 White matter of the spinal cord (myelinated and unmyelinated axons) Ascending fibers: sensory information from sensory neurons of body up to brain Descending fibers: motor instructions from brain to spinal cord Stimulates contraction of body s muscles Stimumulates secretion from body s glands Commissural fibers: white-matter fibers crossing from one side of cord to the other Most pathways cross (or decussate) at some point Most synapse two or three times along the way, e.g. in brain stem, thalamus or other

81 Sensory tracts

82 Motor tracts

83 The spinal cord provides a vital link between the brain and the rest of the body, and yet it exhibits some functional independence from the brain.

84 The adult spinal cord travels from the foramen magnum and terminates within the vertebral foramen of the first lumbar vertebra (L1) in adults.

85 The spinal cord can be subdivided into five regions: cervical region, thoracic region, lumbar region, sacral region, and coccygeal region (which has only one pair of nerves). Don t be confused and think that the sacral region of the spinal cord is surrounded by sacral vertebrae. It is NOT!

86 The diameter of the spinal cord is the largest in the cervical region and there is a larger proportion of white matter compared to gray matter.

87 The diameter of the sacral region of the spinal cord (which is surrounded by the T12/L1 vertebrae) is the smallest and the proportion of gray matter is largest in the spinal cord.

88 The cervical enlargement contains the neurons that innervate the upper limbs The lumbar enlargement contains the neurons that innervate the lower limbs.

89 General Organization Cervical enlargement C5 - T1 Cervical enlargement C5 - T1 Lumbar enlargement L2 - S3

90 The tapering end of the spinal cord is called the conus medullaris. The conus medullaris is surrounded by L1 in and adult and L2 in a child.

91 The adult spinal cord terminates at the level of the first lumbar vertebra (L1) In a developing child, the spinal cord can extend to the level of the second lumbar vertebra (L2)

92 The cauda equina (horse s tail) is composed of nerves that arise from the conus medullaris and extend inferiorly.

93 The filum terminale, which is composed of pia mater, extends from the conus medullaris to the coccyx. Note the subarachnoid space also continues for some distance.

94 There are 31 pairs of spinal nerves that serve defined segments of the human body.

95 There are 8 pairs of cervical spinal nerves. This is possible because the first pair (C1 spinal nerves) exits the spinal column between the occipital bone and the atlas (C1). The remaining 7 pairs (C2- C8 spinal nerves) exit below each of the 7 cervical vertebrae via the intervertebral foramina. All the spinal nerves are mixed nerves.

96 The spinal cord is surrounded by the dura, arachnoid, and pia maters (the meninges)

97 The epidural space is between the vertebra and the dura mater

98 Epidural anesthesia

99 LP (lumbar puncure) = spinal tap (needle introduced into subdural space to collect CSF) Lumbar spine needs to be flexed so can go between spinous processes Originally thought to be a narrow fluid-filled interval between the dural and arachnoid; now known to be an artificial space created by the separation of the arachnoid from the dura as the result of trauma or some ongoing pathologic process; in the healthy state, the arachnoid is attached to the dura and a naturally occurring subdural space is not present. Epidural space is external to dura Anesthestics are often injected into epidural space Injection into correct space is vital; mistakes can be lethal

100 Lumbar Puncture lumbar (terminal) cistern

101 Lumbar Puncture (= Spinal Tap) L3 L4 For clinical examination of CSF or administration of radiopaque dyes, drugs and sometimes anesthetics However: mostly epidurals for anesthetics

102 Epidural anesthesia

103 Effect of epidural anesthesia

104 A person who needs an epidural!

105 The dura mater extends along the entire length of the vertebral canal and surrounds the spinal cord. It also extends along the initial portion of the radiating spinal nerves

106 The subarachnoid space is a real space filled with CSF

107 In this midsagittal picture #3 is the dura mater, #5 is the spinal cord, # 4 is the epidural space, and #6 is the subarachnoid space where CSF is located (#1 is an intervertebral disc and #2 is the body of a vertebrae).

108 Needle for spinal tap

109 Spinal taps are done between the third and fourth lumbar vertebrae because there is no spinal cord at that location

110 The tip of the needle is inserted into the subarachnoid space outside the cauda equina and spinal fluid is removed for testing.

111 The entering pressure can be determined when the needle is inserted into the subarachnoid space during a spinal tap.

112 Spinal fluid is normally crystal clear like water. Cloudy spinal fluid, like the specimen shown, is a sign of white blood cells (pus). The most common cause for white blood cells in the spinal fluid is viral or bacterial meningitis.

113 The pia mater directly adheres to the spinal cord

114 The cross-sectional view shows that the gray matter is central and the white matter is peripheral

115 The peripheral white matter contains ascending and descending tracts of nerves traveling to and from the brain. The central gray matter serves as a center for spinal reflexes.

116 The central canal runs the entire length of the spinal cord, is contiguous with the brain and contains cerebrospinal fluid (CSF)

117 The spinal cord develops as 31 segments, each of which gives rise to a pair of spinal nerves that emerge from the cord through the intervertebral foraminae

118 Nerves can be sensory, motor, or mixed (sensory and motor)

119 Mixed nerves carry both types of information and some axons are transmitting impulses in one direction, while other axons are transmitting impulses in the opposite direction. All spinal nerves are mixed nerves.

120 There are 8 pairs of cervical spinal nerves. This is possible because the first pair (C1 spinal nerves) exits the spinal column between the occipital bone and the atlas (C1). The remaining 7 pairs (C2- C8 spinal nerves) exit below each of the 7 cervical vertebrae via the intervertebral foramina. All the spinal nerves are mixed nerves.

121 Most of the spinal nerves are associated with specific dermatomes (an area of skin innervated by all the cutaneous neurons of a certain spinal or cranial nerve).

122 trigeminal Dermatome map. Note the trigeminal nerve has dermatomes on the face.

123 Dermatomes of the trigeminal nerve (cranial nerve V) are seen on the face

124 Note that the trigeminal nerve has dermatomes on the face (see white area) and that the first pair of cervical spinal nerves (C1 spinal nerves) are not represented on the surface at all.

125 The bony vertebral column (dark line shown) grows faster than the spinal cord. A newborn s spinal cord extends to about the level of L 3. A child s spinal cord may extend to the level of L 2. An adult s spinal cord typically terminates at the level of L 1. Bony vertebral column

126 The inner delicate spinal cord terminates in an adult, as the conus medullaris, at the level of the L 1 vertebra.

127 Damage to the spinal cord can lead to paralysis or death

128 ANTERIOR VIEW OF THE SPINAL CORD CERVICAL CORD (8 nerves) The spinal cord begins at the base of the medulla oblongata and extends to about the 2nd lumbar vertebra. The cord is divided into four regions each of which has branches called spinal nerves. THORACIC CORD (12 nerves) LUMBAR CORD (5 nerves) SACRAL CORD (5 nerves)

129 SAGITAL SECTION OF LOWER SPINE The inferior, terminal portion of the spinal cord is at the level of the 2nd lumbar vertebra. Branches from the lumbar region pass downward from the cone-shaped tip (conus medullaris) of the spinal cord forming the cauda equina (horse s tail). Cauda equina

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131 cranial nerves - 12 pr spinal nerves- 31 pr

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136 Spinal Nerves (31 Pairs) Part of the PNS (Somatic) Lie in intervertebral foramina Send lateral branches to body Named according to their point of issue from the vertebral column 8 pairs of cervical spinal nerves; C 1 -C 8 12 pairs of thoracic spinal nerves; T 1 -T 12 5 pairs of lumbar spinal nerves; L 1 -L 5 5 pairs of sacral spinal nerves; S 1 -S 5 1 pair of coccygeal spinal nerves; C 01

137 Spinal nerves Part of the peripheral nervous system 31 pairs attach through dorsal and ventral nerve roots Lie in intervertebral foramina

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142 Damage below C3 also results in quadriplegia, but the person can still utilize their diaphragm for breathing via their intact phrenic nerves.

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