The Nervous System Notes

Organization of the Nervous System

Nervous system- the master controlling and communicating system of the body 3 functions:

1. Sensory input - sensory receptors to monitor changes occurring inside & outside body2. Integration - processes and interprets the sensory input3. motor output - effects a response by activating muscles or glands (effectors) via motor output

Regulating and Maintaining Homeostasis

nervous system - fast-acting control via electrical impulses endocrine system- slow-acting control via hormones release into the blood

Structural Classification - 2 subdivisions:

Central Nervous System (CNS) - consists of: brain, spinal cord functions:

o integrating center.........interpret incoming sensory informationo command center..........issue instructions based on past experience & current conditions

Peripheral Nervous System (PNS) - consists of o two type of nerves: cranial nerves (carry impulses to and from the brain) and spinal nerves (carry

impulses to and from the spinal cord)o ganglia- groups of nerve cell bodieso function of the PNS: communication lines, linking all parts of the body

Functional Classification (only deals with PNS)

Sensory (Afferent) Division- nerve fibers that carry impulses to the CNS from sensory receptors located throughout body – 2 types

1. somatic sensory fibers- delivering impulses from the skin, skeletal muscles, & joints2. visceral sensory fibers- transmitting impulses from the visceral organs

Motor (Efferent) Division- nerve fibers that carry impulses from the CNS to effector organs ossicles and glands, bringing about a motor response - 2 types:

1. somatic nervous system: conscious control of skeletal muscles2. autonomic nervous system (ANS)- regulates activities that are automatic - 2 types:

sympathetic-” fight or flight” - during extreme situations (ex: increase heart rate, rapid breathing, cold, sweaty skin, dilated pupils)

parasympathetic- “resting & digesting” - most active when body at rest (causing normal digestion, voiding feces & urine, goal: conserving energy)

Nervous Tissue: Structure and function - 2 types of cells: neuroglia and neurons

neuroglia- supporting cells, insulation, & protection, ~90% cells in brain are glial cells, not able to conduct impulses, can undergo cell division, most brain tumors are gliomas- formed by glial cells – see other notes

Neurons - neurons nerve cells that transmit impulses, functional unit of nervous systemo Anatomy (of a generalized neuron) - cell body- metabolic center, contains typical cell organelles

(exception: no centrioles .....no mitosis -amitotic), axon- one per cell, process of neuron that conducts impulses away from the cell body, dendrites- many per cell, extension of neuron that conducts impulses toward cell body (often highly branched), axon hillock- axon arises from this cone like region of cell body, axon terminals- 100’s to 1000’s branches at terminal end of axon that contains vesicles of neurotransmitters

CNS

white matter - dense bundles of myelinated fibers (tracts) brain- inside spinal cord- surface gray matter- unmyelinated fibers and cell bodies brain- surface spinal cord- inside

CNS PNSgroups of cell bodies nuclei ganglia

bundles of nerve fibers tracts nerves

Classification of Neurons

functional classification - according to direction of impulse is traveling relative to CNSo sensory neuron - nerve impulse travels towards CNS, afferent, cell bodies outside CNS in ganglion

receptors - dendrite endings that are specialized activated by specific changes nearby (stimuli): taste, hearing, sight, equilibrium, smell

cutaneous sense organs - pacinian & meissner corpuscles proprioceptors- located in muscles & tendons, detects amount of stretch or tension, determines

location, posture, and tone pain receptors - bare dendrite endings, least specialized cutaneous receptor, most numerous

cutaneous receptoro motor neuron - nerve impulse travels away from CNS

efferent neuron, cell bodies inside CNS in nucleio association neurons (interneurons) - connect motor and sensory neurons, cell bodies in CNS

structural classification - based on number of processes extending from cell bodyo multipolar- several processes, all motor neurons, all association neurons, most common neuron typeo bipolar- 2 process on cell body, axon & dendrite, rare in adults (eg; eye & nose)o unipolar- one process on cell body, single process is very short, process divides into 2:

peripheral process- (distal) contains dendrites on end central process- (proximal) contains axon terminals axon- both peripheral & central processes conducts impulses in both directions (toward & away

from cell body) sensory neurons located in PNS ganglia are all unipolar

Physiology nerve impulse generation (action potential)

reflex arcs - neural pathways involve both CNS & PNS reflexes - rapid, predictable and involuntary responses to stimuli, once reflex begins...always goes in same

direction types:

o somatic reflexes- stimulate the skeletal muscles (eg: pull hand away from hot stove)o autonomic reflexes- regulate the activity of smooth muscles, heart, & glands 9eg: secretion of saliva,

changes in pupil size, regulates: digestion, elimination, blood pressure, & sweating)

Central Nervous System

Functional Anatomy of the Brain – 3 parts – forebrain, midbrain, and hindbraino 1400 grams (3 lbs)o 100 billion neuronso Protected by the cranium, meninges (3 layers) and cerebrospinal fluid

o forebrain - cerebrum & diencephalon (thalamus, hypothalamus, pineal body)o midbrain- small superior part of brain stemo hindbrain - cerebellum, brain stem (part of it)- medulla oblongata, pons

Forebrain o Cerebrum : largest part of brain – 4 lobes

o divided into left and right hemispheres - cerebral hemisphereso the spinal tracts cross over -------> left hemisphere deals w/ right side of body and the right

hemisphere deals w/ left side of bodyo surface is highly convoluted- increasing surface area (increases # of neurons)o cerebral cortex

exterior gray matter, thin surface layer (1-4 mm thick) – highest center of reasoning and intellect Interior- white matter – made of myelinated nerve tracts called white matter, nerve tract

relaying impulses to & from cerebral cortex gyrus (gyri)- elevated ridges on cerebral cortex sulcus (sulci)- shallow grooves in cortex Cerebral cortex - made up of tightly packed neurons and is the wrinkly, outermost layer that

surrounds the brain. It is also responsible for higher thought processes including speech and decision making. The cortex is divided into four different lobes, the frontal, parietal, temporal, and occipital, which are each responsible for processing different types of sensory information such as: speech, memory, logical & emotional response, consciousness, interpretation of sensation, voluntary movement, problem solving, vision and auditory processing

frontal lobe – voluntary motor functions, right hemisphere controls left side movements and the left side controls right side movements; speech

parietal lobe – sensory area – receives and interprets nerve impulses from the sensory receptors for pain, touch, heat, and cold

occipital lobe – eyesight temporal lobe – upper part – auditory, anterior part - olfactory

o Diencephalon - located superior to brain stem & enclosed by cerebral hemispheres – 3 parts thalamus- relay station for sensory impulses passing upward to somatic sensory cortex, all

sensory input passes thru thalamus to cortex (except olfaction), signals from cerebellum pass thru thalamus up to motor area of cortex, encloses 3rd ventricle (spaces filled w/ cerebrospinal fluid...aids in circulation), relay station for incoming and outgoing nerve impulses from various sense organs (not olfactory) and relays them to the cerebral cortex, receives nerve impulses from the cerebral cortex, cerebellum, and other areas of the brain

hypothalamus- below the thalamus, connected to the posterior pituitary gland, thalamus, and the midbrain via nerve fibers - ”seat” of autonomic nervous system, regulates homeostasis for both nervous & endocrine functions, source of 8 hormones, regulation of: body temp, water balance, blood chemistry, metabolism, heart rate, death results if damaged, plays important part in limbic system- “emotional-visceral brain” emotion, motivation, regulates autonomic nervous control, emotional control, store and retains short term memory, “brain” of the brain by stimulating the pituitary to release hormones, appetite control, manufacture oxytocin (uterine contractions during labor), gastrointestinal control, sleep control

epithalamus- forms roof of 3rd ventricle choroid plexus- knots of capillaries w/ in ea. ventricle forms CSF pineal body- endocrine gland - releases melatonin- regulates daily body rhythms (eg: day/ night

cycle melatonin released @ night) Midbrain – small superior part of the brainstem, contains the nuclei for reflex centers involved with vision and

hearing

Hindbrain – cerebellum, brain stem (part of it)- medulla oblongata, ponso Cerebellum – behind the pons and below the cerebrum

2 hemispheres (left an right) that are centrally connected by the vermis Grey matter outside/white matter inside Functions – all body functions to do with skeletal muscles including the inner ear and eye

Balance through the inner ear Maintenance of muscle control Coordinate muscle movements – after initiated by the cerebral cortex, smooth

execution done by the cerebellum (speaking, writing, walking, etc.)o Brainstem – (less the small superior part that makes up the midbrain) provides pathway for the

ascending and descending tracts (messages going to the cerebrum and coming back from the cerebrum) Extending the length of the brainstem is the grey matter of the reticular formation system –

regulates sleep/wake, if damaged can lead to comao Pons – in front of the cerebellum between the midbrain and medulla oblongata

Two way nerve pathway for nerve impulses between the cerebellum, cerebrum, and other nervous system pathways.

4 cranial nerves emerge from here and center controlling respirationo Medulla oblongata – between the pons and the spinal cord – white because its myelinated nerve fibers

serve as a passageway for nerve impulses between the brain and spinal cord Nuclei for heart rate, respiration rate and depth, vasoconstrictor center affecting blood

pressure, center for swallowing and vomiting

Spinal cord – begins at the foramen of the occipital lobe and continues to the 2nd lumbar vertebraeo Inside the vertebrae of the spinal columno Submerged in cerebrospinal fluid and surrounded by 3 meningeso Grey matter inside/white outer portiono In the grey matter, connections made between incoming and outgoing nerve fibers providing the basis

for reflex actionso Reflex center and conduction pathway to and from the brain

Protection of the Central Nervous System

Bones of skull and vertebral column Meninges - 3 continuous sheets covering both spinal cord and brain Cerebrospinal Fluid (CSF) - fluid similar to blood plasma containing protein, vit. C, and ions that bathes cells of

CNS protecting them from physical trauma, returns to blood thru veins draining the brain

Component Function(s)

Cerebellum Long Term Memory Co-ordination (e.g. balance) Muscle Tone Movement Posture

Maintenance of muscle tone, balance, and the synchronization of activity in groups of muscles under voluntary control, converting muscular contractions into smooth coordinated movement.However, it does not initiate movement and plays no part in the perception of conscious sensations or in intelligence.

Cerebrospinal Fluid (CSF)

Bathes the brain and spinal cord Allows nutrients and waste products to diffuse between the blood and the brain / spinal

cord Protects the nerves against mechanical damage

Cerebrospinal fluid is also the subject of cranio-sacral therapy, which is a huge subject in it's own right.

Cerebrum The Cerebrum is also known as the Cortex (Cortex = Cerebrum), and is the largest and most highly developed part of the brain.This is the ‘learning’ part of the brain, and the seat of all intelligent behaviour. It is responsible for the initiation and coordination of all voluntary activity in the body and for governing the functioning of lower parts of the nervous system.

Hypothalamus The hypothalamus is the "Receptor Centre", and "Control Centre" of the body.It contains several important centers controlling body temperature and eating, and water balance. Examples include osmo-receptors that balance water/salt levels and control the water content of the blood. (See diagram opposite.)It is also the Saiety Center (that is concerned with 'satisfaction'), for things like hunger, thirst, sex.It is also closely connected with emotional activity and sleep, and it functions as a center for the integration of hormonal and autonomic nervous activity through its control of the pituitary secretions.The posterior lobe of the pituitary secrets two hormones:

A.D.H. (Anti-diuretic hormone, as known as vasopressin – in U.S.)This works on the kidney tubules. Secretion of ADH tells the kidneys to re-absorb more water, resulting in more concentrated urine. Non-secretion of ADH results in more peeing, and weaker urine.

Oxytocin

Medulla Oblongata

The functions of the medulla oblongata concern the body's involuntary processes, such as: Breathing Heart-rate Swallowing Salivation Vomiting Blinking

The cranial nerves VI – XII leave the brain in this region.

The Meninges Mechanical protection of the brain and spinal column.

Pons Varolii The pons varolii is the part of the brainstem that links the medulla oblongata with the thalamus.

Peripheral Nervous System The peripheral nervous system (PNS) consists of the cranial and spinal nerves that arise from the central nervous

system and travel to the remainder of the body. The PNS is made up of the somatic nervous system that oversees voluntary activities, and the autonomic nervous

system that controls involuntary activities. Cranial Nerves

o Twelve pairs of cranial nerves arise from the underside of the brain, most of which are mixed nerves.o The 12 pairs are designated by number and name and include the olfactory, optic, oculomotor, trochlear,

trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, and hypoglossal nerves.

Spinal Nerves o Thirty-one pairs of mixed nerves make up the spinal nerves.o Spinal nerves are grouped according to the level from which they arise and are numbered in sequence, beginning

with those in the cervical region.o Cervical Plexuses lie on either side of the neck and supply muscles and skin of the neck.o The brachial plexuses arise from lower cervical and upper thoracic nerves and lead to the upper limbs.o The lumbrosacral plexuses arise from the lower spinal cord and lead to the lower abdomen, external genitalia,

buttocks, and legs.

Autonomic Nervous System The autonomic nervous system has the task of maintaining homeostasis of visceral activities without conscious effort. consists of motor neurons that control smooth muscles, cardiac muscles, and glands; monitors visceral organs and blood

vessels with sensory neurons, which provide input information for the CNS Control of Autonomic Activity

o The autonomic nervous system is largely controlled by reflex centers in the brain and spinal cord.o The limbic system and cerebral cortex alter the reactions of the autonomic nervous system through emotional

influence. Two divisions

o Sympathetic and parasympathetic divisions, which exert opposing effects on target organs.o The effects of these two divisions, based on the effects of releasing different neurotransmitters to the effector, are

generally antagonistic. Sympathetic Division - operates under conditions of stress or emergency

o Fibers in the sympathetic division arise from the thoracic and lumbar regions of the spinal cord, and synapse in paravertebral ganglia close to the vertebral column.

o Postganglionic axons lead to an effector organ.o prepares the body for situations requiring alertness or strength, or situations that arouse fear, anger,

excitement, or embarrassment (“fight‐or‐flight” situations) - stimulates cardiac muscles to increase the heart rate, causes dilation of the bronchioles of the lungs (increasing oxygen intake), and causes dilation of blood vessels that supply the heart and skeletal muscles (increasing blood supply). The adrenal medulla is stimulated to release epinephrine (adrenalin) and norepinephrine (noradrenalin), which in turn increases the metabolic rate of cells and stimulates the liver to release glucose into the blood. Sweat glands are stimulated to produce sweat. In addition, the sympathetic nervous system reduces the activity of various “tranquil” body functions, such as digestion and kidney functioning.

Parasympathetic Division - operates under normal conditions.o Fibers in the parasympathetic division arise from the brainstem and sacral region of the spinal cord, and

synapse in ganglia close to the effector organ.o Active during periods of digestion and rest. It stimulates the production of digestive enzymes and

stimulates the processes of digestion, urination, and defecation. It reduces blood pressure and heart and respiratory rates and conserves energy through relaxation and rest.

o Autonomic Neurotransmitters o Preganglionic fibers of both sympathetic and parasympathetic divisions release acetylcholine.o Parasympathetic postganglionic fibers are cholinergic fibers and release acetylcholine.o Sympathetic postganglionic fibers are adrenergic and release norepinephrine.

Somatic Nervous System The somatic nervous system includes the sensory input and the motor innervation to most of the body, except for the

organs, smooth muscles, and glands. It deals with the parts of the body you can move voluntarily. Sensory neurons transmit sensory information from the skin, skeletal muscle, and sensory organs to the central nervous

system (CNS). Motor neurons transmit messages about desired movement from the CNS to the muscles, causing them to contract. Without its sensory-somatic nervous system, an animal would be unable to process any information about its environment

(what it sees, feels, hears, etc.) and could not control motor movements.

Nervous System: Special Senses – Not Completed Yet

The nervous system responds to external signals through nerve cells or nerve fibers (neurons). Surface and external receptors also feed signals into the system from the environment.

Sensations from the external environment are collected and sent to the CNS from receptors through sensory neurons.

The special senses (smell, taste, eye, ear and balance) play a significant role serving as receptors that collect and transmit external sensations from the environment to the brain.

Sensation - sense of awareness to changeso detect changes in the external environmento respond to the changeso maintain homeostasis

Pathways of Sensationo Receptors on the skino Sensory neurons carry the messageo Sensory tracts involve the white matter in CNSo Sensory area (cerebral cortex feels and interprets sensation)

THE EYEo Sclera - outer layer or white of eyeo Cornea - center and front of sclerao Choroid coat - middle of the eyeo Iris - colored, muscular part o Pupil - circular opening in iriso Lens - behind iris and pupilo Retina - innermost (third) coato PATHWAY OF VISION

THE EARo The outer ear collects sound waves and directs them into auditory canalo The middle ear equalizes air pressureo The inner ear fluid-filled duct vibrates with sound waves

THE NOSEo The human nose can detect about 10,000 different smells

THE TONGUEo The tongue is a mass of muscle tissue with structures called papillaeo Taste buds cover the papilla, which are stimulated by sweet, sour, salty, and bitter tastes