Nervous System. Overview, Tissues and Spinal Nerves

Transcription

1 Nervous System Overview, Tissues and Spinal Nerves

2 neurology - study of the nervous system - nervous system and endocrine system work together to maintain homeostasis - More than 80 major nerves and billions of neurons (individual nervous cells)

3 Nervous System - works very fast - Uses electrical signals called nerve impulses which are short lived - Ex.; knee jerk reflex Endocrine System - works slowly - Uses chemical messengers called hormones whose responses last a long time - Ex.; reproductive cycle

4 Structures of the Nervous System 1. Neuron - cell of the nervous system 2. Nerve - bundle of neurons with connective tissue and blood vessels 3. Brain - contained in the skull; contains 100 billion neurons 4. cranial nerves - 12 pairs, emerge from the base of the brain and each serves a specific region of the body

5 Structures of the Nervous System (cont) 5. spinal cord - connects to the brain through a large opening in the skull called the foramen magnum - Encircled by bones of the vertebral column - Contains 100 million neurons 6. spinal nerves - 31 pairs, each serving a specific region on the body

6 Structures of the Nervous System (cont) 7. ganglia - small masses of nervous tissue located outside the brain and spinal cord 8. enteric plexus - in walls of gastrointestinal tract; help regulate digestive system 9. sensory receptors - monitor changes in the internal or external environment

7 Functions of Nervous System 1. Sensory Function - sensory receptors detect both internal & external stimuli & carry that info to the brain via sensory (afferent) neurons 2. Integrative Function - processes the info received and acts on it through interneurons (the majority of neurons in the body) 3. Motor function -motor (efferent) neurons carry info from brain and spinal cord to effectors (cells and organs that respond to the integrative decisions)

8 Branches of the Nervous System 1. Central Nervous System (CNS) - brain & spinal cord - integration of sensory information - the source of thoughts, emotions, & memories 2. Peripheral Nervous System(PNS)-relay station to CNS - includes all nervous tissue outside of CNS, cranial nerves & branches, spinal nerves & branches, ganglia & sensory receptors - Further divided into Somatic, Autonomic and Enteric Nervous System

9 Somatic Nervous System (SNS) - Under voluntary control - Sensory neurons send message to the brain - Motor neurons send impulses to skeletal muscle only

10 Autonomic Nervous System (ANS) - Involuntary - Sensory receptors located in the chest and abdomen - Motor neurons send message to smooth and cardiac muscle - Further divided into Sympathetic and Parasympathetic divisions

11 Autonomic Nervous System (ANS) Sympathetic division - stimulates functions (ex. Increases heart rate) Parasympathetic division - inhibits functions (ex. Decreases heart rate)

12 Enteric Nervous System (ENS) - Brains of the gut - Involuntary - Controls digestive system

13 Types of Nerve Cells 1. neurons - functional cell of the nervous system - responsible for thinking, sensing, remembering, controlling muscle activity and regulating glandular secretions - communicate using both electrical & chemical signals 2. neuroglia - glue of the nervous system - support, nourish and protect the neurons

14 Parts of a Neuron 1. soma - the cell body; contains a nucleus with organelles 2. dendrites - little trees ; receive messages (bring action potential in from previous neuron 3. axon - carries messages to the next neuron, muscle or gland - joins the cell body at the axon hillock

15 Parts of a Neuron (cont.) 4. Schwann cells - cells that wrap themselves around the axon - Forms the myelin sheath which protects the neuron and speed up the action potential - myelin - insulating tissue composed of lipids that speeds up nerve impulses (not all nerves have myelin)

16 5. nodes of Ranvier - gaps in between myelinated sections (do not contain myelin!) 6. neurolemma - covering of myelin sheath ONLY in the PNS (covering of the Schwann cell); helps regenerate injured axons - Since CNS lacks neurolemma, they cannot regenerate after an injury

17 How do neurons communicate? synapse - space between neurons, or between a neuron and muscle or cell, where communication occurs synaptic end bulbs - at the tip of the axon terminal - end in little sacs called synaptic vesicles, which contain chemical neurotransmitters that influence activity of neurons, muscles or glands

18 Neurotransmitters Acetylcholine - slows heart rate Glutamate, aspartate - powerful excitatory effects Gamma aminobutyric acid (GABA), glycine - inhibitory effect (anti-anxiety meds are GABA agonists...enhance the action of GABA)

19 Neurotransmitters (cont) Epinephrine, norepinephrine - involved in waking from deep sleep, dreaming and regulating mood Dopamine - emotional response & some aspects of movement Serotonin - involved in sensory perception, temperature regulation, controls mood and sleep induction

20 Nerve Impulse Propagation Spinal cord conducts impulses along tracts 1. Sensory receptor - responds to a stimulus 2. Sensory neuron - also called afferent neuron; axon conducts impulse from receptor to the integrating center 3. Integrating center - relays the impulse from the sensory neuron to the motor neuron 4. Motor neuron - also called efferent neuron; axon conducts the impulse from the integrating center to the effector 5. Effector - muscle or gland that responds to motor nerve impulse

21 White Matter white matter - groups of myelinated processes from many neurons -in spinal cord, for nerve impulse propagation; sensory impulses flow from body to brain, motor impulses flow from brain to body

22 Gray Matter gray matter - contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals and neuroglia - in spinal cord, to receive and integrate incoming and outgoing info

23 Coverings of the Spinal Cord spinal meninges - connective tissue coverings that encircle the spinal cord 1. Dura mater - tough, outer layer (leather like). Arachnoid - middle layer; has a spider-web appearance. Pia mater - innermost layer that adheres to the spinal cord

24 meningitis - inflammation of spinal meninges spinal tap - needle inserted into subarachnoid space in adults (usually between 3rd and 4th lumbar vertebrae)

25 Spaces in spinal cord Subarachnoid space - located between the arachnoid and pia mater; contains cerebrospinal fluid (CSF) Subdural space - located between the dura mater and arachnoid; contains interstitial fluid Epidural space - cushion of fat and connective tissue located between the dura mater and the wall of the vertebral canal

26 Vertebral Column -spinal cord is located within the vertebral canal (formed by the vertebral foramina) of the vertebral column - spinal cord is the link between the brain and the nerves

27 Cerebrospinal Fluid -a clear, colorless liquid that circulates continuously in the subarachnoid space around the brain and spinal cord - function is to act as a shock absorber and for the exchange of nutrients/waste - provides the optimal environment for nerve impulses to travel

28 cauda equina - roots of inferior spinal nerves Spinal cord -extends from the medulla oblongata (most inferior part of the brain) to the second lumbar vertebra cervical and lumbar enlargements - can be seen where nerves from the upper and lower limbs arise conus medullaris - where spinal cord tapers filum terminale - extension of the pia mater that anchors the spinal cord to the coccyx

29 Spinal nerves -paths of communication between spinal cord and nerves innervating specific regions of the body Roots - connect each spinal nerve to the spinal cord - Posterior root - contains sensory fibers that conduct impulses into the CNS - Anterior root - contains motor neurons that conduct impulses from CNS to effectors

30 Spinal nerves (cont) -31 pairs - part of peripheral nervous system - connect the CNS to sensory receptors, muscles and glands

31 Spinal nerve coverings epineurium - superficial covering over the entire nerve perineurium - covering of fascicles, which are bundles of axons endoneurium - covering of individual axons

32 Cervical Plexus -supplies skin and muscles of the head, neck and superior part of shoulders and chest Sensory branches - lesser occipital (scalp), transverse cervical (anterior neck), supraclavicular (chest & shoulder) Motor branches - ansa cervicalis (neck), phrenic (diaphragm)

33 ulnar (medial forearm and hand) nerves Brachial Plexus -provides entire nerve supply of shoulders and upper limbs axillary (deltoid muscle); musculocutaneous (flexors); radial (back of upper arm and forearm); median (anterior forearm and hand); and

34 -thoracic nerves Intercostal Nerves -T2 - innervates axilla and back of arm - T3-T6 - intercostal muscles and skin of anterior and lateral chest -T7-T12 - intercostal muscles and abdominal muscles

35 Lumbar Plexus -supplies anterolateral abdominal wall, external genitals and lower limbs iliohypogastric (ab muscles, skin of abs & butt) ilioinguinal (ab muscles,thigh skin,external genitals) genitofemoral (genitals) lateral femoral cutaneous (skin of thigh) femoral (thigh muscles and skin of thigh, medial leg & foot); obturator (adductor muscles of leg, skin of thigh)

36 Sacral Plexus -supplies the butt, perineum and lower limbs superior gluteal (glutes) inferior gluteal (gluteus maximus) nerve to piriformis (piriformis muscle) sciatic - made up of tibial (back of leg) and common peroneal (front of leg) posterior femoral cutaneous (skin of anal region, lower butt) pudendal (muscles of perineum, skin of genitals)

37 Dermatomes -the area of skin that provides sensory input via the posterior roots of one pair of spinal nerves -makes it possible to locate damaged regions of the spinal cord (pricking areas of body with a pin) - also used for anesthetics

38 Spinal cord transection -an injury that entirely severs the spinal cord resulting in permanent loss of sensation below the injury -the location of the transection determines the extent of paralysis

39 Spinal cord transection C1-C3- paralysis from neck down, ventilator needed C4-C5 - diaphragm, which allows breathing C6-C7- some arm and chest function T4-T9 - control of trunk above umbilicus

40 Disorders neuritis - inflammation of one or several nerves resulting from direct blows, fractures, contusions, penetrating injury, infections, vitamin deficiency or poisoning

41 Disorders (cont) shingles - acute infection of the PNS caused by the herpes zoster virus - Normally it is dormant in the posterior root ganglion...if activated, it travels down the sensory neuron resulting in pain, discoloration of skin and a line of blisters

42 poliomyelitis - polio Disorders (cont) - Caused by poliovirus - Fever, severe headache, stiff neck and back, deep muscle pain and weakness - Destroys cell bodies of motor neurons resulting in paralysis

43 - Strikes between the age of 20 and 40, females twice as often as males - Symptoms include a heaviness or weakness in the muscles, abnormal sensations, double vision - Progressive loss of function Disorders (cont) Multiple sclerosis - progressive destruction of myelin sheaths of neurons in the CNS; myelin sheaths sclerose (harden) in multiple locations

44 Disorders (cont) epilepsy - short, recurrent, periodic attacks of motor, sensory or psychological malfunction - Attacks are initiated by abnormal synchronous electrical discharges from millions of neurons in the brain - Results in involuntary skeletal muscle contraction (seizure) - Most epileptic seizures are idiopathic

45 Disorders (cont) Amyotrophic lateral sclerosis - rare, progressive, neurodegenerative disease that causes the death of neurons responsible for controlling voluntary muscle movement - Also called Lou Gehrig s disease - Loss of muscle control to all parts of the body, including breathing - Usually death within 5 years of diagnosis

46 Disorders (cont) Acute flaccid myelitis - affects the grey matter of the spinal cord - Causes muscle weakness, loss of muscle tone, slurred speech

47 Disorders (cont) Guillain-Barre - disorder where the body s immune system attacks nerves - Starts with weakness and tingling and progresses to paralysis of entire body - Usually preceded by an infection or illness

48 - A Guillian-Barre story: Holly