Biology Unit 1: Nervous System

Transcription

1 Biology 3201 Unit 1: Nervous System

2 Nervous System Pre-Lesson Work: - Create a concept map about the human nervous system.

3 1. Brain What are the major parts of the 2. Spinal Cord Nervous System? 3. A series of neurons that transmit impulses throughout the body.

4 The Nervous System

5 What is the function of the Nervous System - To help maintain homeostasis (remembersteady internal state). - It does this by regulating body temperature, blood-glucose levels, motor coordination, among other body processes.

6 Structures of the Nervous System: There are two main sections: 1. The Central Nervous System (CNS): The Brain The Spinal Cord 2. The Peripheral Nervous System (PNS): - The nerves that lead into and out of the central nervous system

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8 Function of the CNS: To receive sensory information, interpret that information and initiate responses such as motor responses.

9 Protection of the CNS: Four structures are used to protect the CNS. They include (i) the skull (ii) the vertebrae (iii) meninges (iv) the cerebrospinal fluid. The skull forms an enclosure around the brain and the vertebrae enclose the spinal cord. Meninges are protective membranes that surround both the brain and spinal cord. The cerebrospinal fluid fills the spaces within the meninges to create cushion and provide further protection.

10 Protection of CNS

11 The Spinal Cord The function of the spinal cord is to provide communication between the brain and the peripheral nervous system (PNS). The spinal cord extends from the vertebrae in the back though the bottom of the skull into the base of the brain. Spinal nerves will pass through the vertebrae and out to the PNS.

12 Spinal Cord Structure: A cross section of the spinal cord show the (i) central canal containing cerebrospinal fluid (ii) grey matter and (iii) white matter. See fig 12.3 p. 393.

13 Grey Matter and White Matter The grey matter is brownish-grey in color and contains sensory neurons, motor neurons and interneurons. It also contains cell bodies and non-myelinated fibres. The grey matter is found in the center of the spinal cord in the form of a letter H. The white matter is found around the grey matter. It contains the myelinated axons of interneurons that run together in tracts. Ascending tracts carry information to the brain whereas descending tracts carry information from the brain.

14 The Brain The brain is thought to be made up of nearly 100 billion neurons and is the most complex organ if the human body. It is responsible for controlling every process in your body as well as gathering, interpreting and reacting to information and conditions of the external environment.

15 The Brain- 4 Lobes

16 Lobes of the Brain Frontal- thinking, planning, problem solving and decision making Parietal- perception, organization, classification Temporal- memory, hearing, language, speech and emotion Occipital- vision, visual processing and colour identification

17 The Brain- 2 Hemispheres

18 Structure and Function of the Brain Cerebrum Controls complex behaviour and intelligence. Makes decisions and stores memories. Controls voluntary muscles (ones you can consciously move). Collects info from our senses and sorts it. Makes us different from other mammals (we have more cerebrum tissue). Very convoluted to increase surface area.

19 Cerebrum

20 Cerebellum Controls motor coordination and balance. Contains 50% of the brains neurons. The physical skills we learn are slowly taken over by the cerebellum and are not consciously controlled, eg. Walking, running, etc.

21 Medulla Controls involuntary life processes, heart rate, blood pressure, breathing rate. Swallowing, hiccuping, vomiting, coughing.

22 Thalamus Sensory relay center Receives sensations of heat, touch, pain, cold as well as info from muscles. Relays mild sensations to cerebrum Relays strong sensations for immediate action to the hypothalamus.

23 Hypothalamus Hypothalamus acts as the main control center for the autonomic nervous system. Controls the sympathetic and parasympathetic responses. Controls hunger, temperature, aggression and other aspects of metabolism and behavior.

24 Midbrain Short section of brainstem between the cerebrum and the pons. It is involved in sight and hearing.

25 Pons contains bundles of axons traveling between the cerebellum and rest of CNS. It works with the medulla to regulate breathing rate and has reflex centers involved in head movement.

26 Corpus Callosum is a series of nerve fibers that connects the left and right hemispheres of the brain.

27 Neurons and The Reflex Response Structure of a neuron:

28 Structures of the Neuron Dendrites- the primary site for receiving signals from other neurons Cell body- the main part of the neuron that contains the nucleus and other organelles for cell function. Axon- A long extension of the cell body that can be up to 1 meter in length. It transmits impulses along its length. Schwann Cells- these are supportive cells that extend the length of the axon, producing a myelin sheath. The gap between each schwann cell is called a node.

29 Myelin Sheath- an insulating layer that surrounds the axon and helps the neuron transmit impulses quickly and efficiently. Axon Terminal- the end of the axon where specialized structures call vesicles are located. These vesicles contain chemicals that can either stimulate or inhibit a neighbouring neuron.

30 Three Classes of Neurons 1. Sensory Neuron- take information from a sensory receptor, such as a pain receptor, to the CNS. 2. Interneuron- receives info from sensory neurons and other interneurons and exchanges the information among neurons in the CNS. 3. Motor neuron- takes info from the CNS to an effector, such as a muscle fiber or gland.

31 Receptors vs Effectors Receptors Effectors Take in stimuli (pain, smell, etc.) from the environment. Ex: Skin receptors are stimulated by pain, heat, cold, pressure, touch The muscles and glands of the body that carry out actions as instructed by the CNS. Ex: pulling your hand out of hot water. Other receptors include the sensory organs: nose, eyes, ears and tongue

32 What is a Reflex? When a certain action sets off a specific reaction automatically. Ex: Blinking when something moves close to your eye.

33 The Reflex ARC

34 LAB #1 Answer the pre-lab question. Do a complete lab write-up: Title, Problem, Hypothesis, Materials, Procedure, Observations (table), Discussion (answer questions), Conclusion. Pass in your lab report either in a lab notebook or a duotang folder. DUE:

35 How the Neuron Works 1. At Rest Not carrying an impulse. Membrane surface is polarized (overall positive charge on outside, negative charge on the inside). The difference in charge between the inside and outside is approximately -70 mv, this is the resting potential. The overall positive charge on the outside of the axon is due to the excess of sodium(na + ). The overall negative charge on the inside is due to excess of anions. Embedded in the lipid bilayer of the axon wall are gated channels through which sodium and potassium move during and following an impulse.

36 All-Or-None Principle If an axon is stimulated sufficiently (above the threshold), the axon will trigger an impulse down the length of the axon. The strength of the impulse will be uniform along the entire length of the axon. The strength of the response is independent of the strength of the stimulus.

37 2. Depolarization If the neuron is sufficiently stimulated, a wave of depolarization is triggered. This involves sodium channels opening and potassium channels closing. Sodium moves inside, making the inside more positively charged than the outside. This change in charge is called Action Potential, and starts a chain reaction of depolarization down the length of the axon.

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39 3. Repolarization (2 steps) Immediately after the Na channels have opened for depolarization, the gates of K channels re-open, Na channels close and K ions move out. This re-establishes the polarization in the area. To restore the resting ion distribution, the Na/K pump actively transports Na back outside the membrane.

40 The mitochondria in the neuron uses oxygen and glucose to produce ATP, which releases the energy that fuels the Na/K pump. Immediately after the wave of polarization, there is a refractory period- approx s before the axon is ready for another impulse.

41 Impulse Transmission and Membrane Potential The membrane potential refers to the voltage that is measured before, during and after the impulse passes. Resting Potential is 70 mv. The negative signs refers to the difference in charge between the inside and outside of the axon. It is more negative inside, hence, the 70.

42 Depolarization- As the sodium ions flood in, the charges switch and therefore the voltage increases to approximately +40 mv. Repolarization- As the potassium moves outside the axon, the voltage decreases to just below resting potential (hyperpolarized). Then rises back to resting (-70mV).

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45 Impulse Transmission and Membrane Potential The membrane potential refers to the electrical activity that is measured before, during and after the impulse passes. Resting Potential is 70 mv. The negative signs refer to the difference in charge between the inside and outside of the axon. It is more negative inside, hence, the 70. Depolarization- As the sodium ions flood in, the charges switch and therefore the voltage increases to approximately +40 mv. Repolarization- As the potassium moves outside the axon, the voltage decreases to just below resting potential (hyperpolarized). Then rises back to resting (-70mV).

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47 What happens when the impulse reaches the end of the neuron? The transmission will either continue down the neighbouring neuron, or stop. It depends on the neurotransmitters (chemicals) that are released from the vesicles at the axon terminal. When the impulse reaches the axon terminal, a neurotransmitter is released into the gap (synapse) that is between neighbouring neurons.

48 The Synapes

49 Neurotransmitter

50 Synapses Neurons do not touch one another; there are tiny gaps between them. These are synapses. Presynaptic neuron- the neuron that carries the wave of depolarization towards the gap. Postsynaptic neuron- the neuron that receives the stimulus.

51 What happens at the Synapse? When the wave of depolarization reaches the end of the presynaptic axon, it triggers the opening of special calcium gates. The presence of calcium triggers the release of neurotransmitters from synaptic vesicles, which are located at the ends of the axon.

52 The neurotransmitter diffuses into the synapse and causes either an excitatory or inhibitory response. Excitatory response involves the opening of sodium channels in the post-synaptic neuron triggering the wave of depolarization. Inhibitory response will cause the impulse to stop. It does this by opening chloride channels and causing the inside of the membrane to be more negative.

53 The Importance of Neurotransmitters

54 Importance of Cholinesterase Cholinesterase is an enzyme that works in conjunction with acetylcholine. After the acetylcholine has binded to the receptors on the postsynaptic neuron and has produced it s desired effect, cholinesterase is released from the pre-synaptic neuron to break down the acteylcholine and bring the neuron back to rest.

55 STSE Drugs and Homeostasis

56 Diseases associated with the Nervous System Give a description of the disease, causes, effects and treatments of. Meningitis Multiple Sclerosis Alzheimers Parkinson s Huntington s

57 Technology Used to Diagnose and Treat N.S diseases 1. MRI- Magnetic Resonance Imaging Scans the brain using a combination of large magnets, radio frequencies and computer aids to produce a detailed image of the brain or body. Under the influence of the magnetic field the protons of hydrogen atoms in the body line up parallel to each other. The atoms have entered a high-energy state and are unstable.

58 A strong pulse of radio waves is used to knock the protons out of alignment. As the protons realign themselves, they return to a low energy state and they produce radio signals that the computer converts into a 2D or 3D image. See youtube video: Understanding MRIs

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60 2. EEG- Electroencephalogram Measures electrical impulse activity of the various areas of the brain. Pioneered by canadian Dr. Wilder Penfield. Monitors the condition of patients during surgery. Can be used to determine brain death. Can diagnose disorders such as brain tumors and epilepsy. Used to study brain activity during sleep to help doctors diagnose and understand sleep disorders

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62 3. CAT scan- computerized Tomography Takes cross sectional x-rays to create a 3D image of a part of the body. Can be rotated and viewed slice by slice to look for abnormalities.

63 The EYE

64 The Eye- Three Layers (I) Sclera is a thick, white outer layer that gives the eye its shape. At the front of the eye where the sclera bulges out and becomes clear is the cornea. The thin, transparent membrane which covers the cornea and is kept moist from fluid from the tear glands is the conjunctiva.

65 (II) Choroid layer is the middle layer of the eye which absorbs light (which has not been absorbed by the sclera) and prevents internal reflection. At the front of the eye, it becomes the iris (opens and closes to control the size of the pupil). The pupil is the opening in the center of the iris of the eye which allows light to enter the eye. The lens is the structure behind the iris that focuses light on the retina.

66 (III) Retina or inner layer of the eye is composed of two types of photoreceptors: (A) rods (more sensitive to light than cones but unable to distinguish colours) and (B) cones (require more light than cones to be stimulated but are able to detect red, green, and blue). Cones are not evenly distributed on the retina. They are concentrated in an area called the fovea centralis which is directly behind the center of the lens.

67 Chambers of the Eye Anterior chamber is between the cornea and the lens and is filled with a transparent watery fluid called the aqueous humour. It is like a pre - lens which initiates the process of focusing an image on the retina before it encounters the lens. The posterior compartment is behind the lens and is filled with a clear gel called the vitreous humour and helps to maintain the shape of the eyeball.

68 Structures of the Eye 1. Cornea is the clear, dome-shaped tissue covering the front of the eye. 2. Iris is the colored part of the eye. It controls the amount of light that enters the eye by changing the size of the pupil. 3. Lens is a crystalline structure located just behind the iris. It focuses light onto the retina. 4. Optic nerve is the nerve that transmits electrical impulses from the retina to the brain. 5. Pupil is the opening in the center of the iris. It changes size as the amount of light changes (the more light, the smaller the hole). 6. Retina is the sensory tissue that lines the back of the eye. It contains millions of photoreceptors (rods and cones) that convert light rays into electrical impulses that are relayed to the brain via the optic nerve. 7. Vitreous is a thick, transparent liquid that fills the center of the eye. It is mostly water and gives the eye its form and shape; (also called the vitreous humour).

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70 How the Eye Works: (1) Light enters the eye. (2) It passes through the cornea, aqueous humour, pupil, lens and vitreous humour and forms an image on the retina.(if there is too much light present the pupil constricts and dilates if light is insufficient.) (3) The retina has three cell layers (ganglion cell layer, bipolar cell layer, and the rod and cone cell layer). Bipolar cells synapse with rods and cones and transmit impulses to ganglion cells. Ganglion cells join together and form the optic nerve as they exit the eye. Optic nerve carries the impulse to the brain. Blind spot is the - point where the optic nerve leaves the eye

71 Eye Disorders 1. Glaucoma 2. Astigmatism 3. Hyperopia 4. Myopia 5. Cataracts 6. Lazy Eye

72 Treatment 1. Laser Surgery PRK and LASIK 2. Corneal Transplant

73 The Ear

74 The Human Ear The ear is also a homeostatic organ. It has mechanoreceptors that translate movement of air into a series of nerve impulses that the brain is able to interpret as sound. It is divided into three separate sections: (1) outer ear ; (2) middle ear ; and (3) inner ear.

75 (1) Outer ear pinna and auditory canal : Auditory canal contains tiny hairs and sweat glands, some of which are modified to secrete earwax that protects the ear from foreign particles.

76 2) Middle ear begins at the tympanic membrane or eardrum and ends at two small openings called the round window and the oval window. Between the tympanic membrane and the oval window are the three smallest bones: (a) malleus (hammer) ; (b) incus (anvil) and (c) stapes (stirrup). These three bones comprise the ossicles. Between the middle ear and the nasopharynx is the auditory tube or the Eustachian tube.this tube allows ear pressure to equalize, and in elevators and airplanes, yawning can cause the air to move through the Eustachian tube and the ear will pop.

77 (3) The inner ear consists of three sections : (a) cochlea (involved in hearing) ; (b) vestibule (balance and equilibrium) ; (c) semicircular canals (balance and equilibrium).

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79 How We Hear (1) Sound waves enter the auditory canal. (2) Sound waves cause the tympanic membrane to vibrate. (3) These vibrations pass across the tympanic membrane to the malleus, which causes the incus and the stapes to move. (4) The stapes passes the vibration to the membrane of the oval window, which passes it through to the fluid within the cochlea.

80 (5) The cochlea is a coiled canal in the dense bone tissue of the skull. The shape of this canal somewhat resembles a snail shell and houses three fluid-filled membranous canals extending its full length. The central canal houses the "ORGAN OF CORTI" which is comprised of specialized cells and their supporting tissues. Vibratory energy propagated through the fluid produces deformation of the organ of Corti, in turn resulting in shearing forces on tiny tufts of "hairs" or cilia extending from the upper surfaces of the "hair cells." This shearing action triggers an electrochemical signal that travels upward through the auditory nervous pathway which passes through the internal auditory canal to the brainstem and then upward to the auditory processing centers in the temporal lobes of the brain. This is a simplified description of a fascinatingly complex activity that ultimately results in "hearing."

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82 Ear Disorders: (I) Nerve deafness is caused by damage to hair cells in the spiral organ. Hearing loss is usually uneven, with some frequencies more affected than others. It usually happens with aging and cannot usually be reversed. (II) Conduction deafness is caused by damage to outer or middle ear that affects the transmission of sound waves to the inner ear. It can be improved with hearing aids.

83 Treatments: 1. Hearing Aids: A. Conventional B. Programmable 2. Eustachian Tube Implants

84 Ethical Issues for auditory and visual disorders (1) Surgery may exclude a person from the deaf community that communicates in sign language. (2) There are few donor cornea available for transplant. Should there be mandatory donation?

85 Stroke and Spinal Injury A stroke is a sudden loss of brain function. It is caused by the interruption of flow of blood to the brain (ischemic stroke) or the rupture of blood vessels in the brain (hemorrhagic stroke). Treatment? Clot-busting drugs Surgery to remove pools of blood

86 Treatment of Spinal Injury Treatment starts with steroid drugs to reduce inflammation in the injured area and prevent further damage to cellular membranes that can cause nerve death.

87 Each patient's injury is unique. Some patients require surgery to stabilise the spine, correct a gross misalignment, or to remove tissue causing cord or nerve compression. Some patients may be placed in traction and the spine allowed to heal naturally.

88 Importance of Glucose to N.S Cells within the nervous system require enormous amounts of energy to function. This energy is provided by the processing of glucose and the production of ATP within these tissues, requiring an adequate supply of carbohydrates and oxygen (Na+/K+ pump). ATP energy is required to operate the sodium-potassium pump which convert cellular chemical signals into electrical signals along a nerve cell and in between individual nerve cells (i.e., synapse).