NERVOUS SYSTEM

Homeostasis controlled by

• Nervous system

• Endocrine system

Divisions of the nervous system

• Central nervous system (CNS)

• Spinal cord• brain

• Peripheral Nervous system (PNS)

• Nerves that carry impulses to and from CNS

Functions

• Monitoring changes inside and outside of body – (stimuli) and gathers sensory input

• Integration – processes and interprets the sensory input and makes decision about what is to be done

• Effects a response by activating a muscle or gland – response is called motor output

Neuron

Nerve cell

Parts of a neuron

• Dendrite – carries impulses to the cell body• Axon – carries impulses from the cell body• Myelin sheath – protective layer formed by

Schwann cells• Nodes of Ranvier – gaps between the

sheaths ( not present in all neurons)• Axonal terminals – branches located at the

terminal end of the neuron

• Neurilemma – sheath of Schwann

• Collateral branch – branch arising from the axon ( not present in all axons)

• Oligodendrocytes – take the place of the Schwann cells in the CNS

SUPPORTING CELLS - neuroglia

• Astrocytes – numerous projections with swollen ends that cling to neurons. Anchoring the neurons to their blood supply

• Microglia – phagocytes that dispose of debris such as dead brain cells, bacteria, ect.

• Ependymal cells = line cavities of the brain and spinal cord. Have cilia that beat to circulate the cerebrospinal fluid

• Oligodendrocytes• Satellite cells – protective and cushion nerve cells

TYPES OF NEURONS

1. Afferent

• Also called sensory

• Carry nerve impulses toward CNS

2. Efferent

• Also called motor neuron

• Carries impulses away from CNS

3. Interneuron

• Also called association neuron

• Connect motor and sensory neuron in neural pathways

CONDUCTION OF A NERVE IMPULSE

RESTING POTENTIAL

• Membrane is polarized• Not conducting an impulse• -65mV to –70 mV• Na+ greater concentration on outside• K+ greater concentration on inside• Overall charge is + on outside and – on inside• Na/K pumps maintains this difference

DEPOLARIZATION

• Activates the neuron to transmit and action potential (AP) also called a nerve impulse

• All or nothing response – AP is either propagated or not

• Threshold must be reached –55mv• Na+ gates open and Na+ flows inside

neuron• Voltage changes from –65 to +40

REPOLARIZATION

• Na+ gate closes

• K+ gate open and K+ flows to outside

• Voltage change from +40 to –65

• Na/K pumps return Na+ and K+ back to normal

• Thus neuron returns to resting potential

REFRACTORY PERIOD

• AP has passed

• Na gate can’t open

• Keeps AP from traveling in the wrong direction

CROSSING THE SYNAPSE

• Synapse – gap between the presynaptic and postsynaptic membrane

• AP arrives at the presynaptic membrane

• Presynaptic membrane becomes permeable to Ca++

• Vesicles move to the presynaptic mb.

• They release neurotransmitter

Myelinated neurons

• Conduction occurs faster because the nerve impulses jump from node to node along the length of the fiber

• Saltatory conduction – faster conduction in myelinated neurons

External impairment of conduction

• Alcohol, sedatives, and anesthetics block nerve impulses by reducing membrane permeability to sodium ions

• Is no Na ions can enter the neuron then no AP will occur

• Cold and pressure hinder impulse conduction because the interrupt blood circulation

• Neurotransmitter diffuses across the synaptic cleft

• At the postsynaptic mb. The neurotransmitter merges with receptor sites

• AP starts at the postsynaptic mb

• Neurotransmitters may be broken down by enzymes, washed away, or recycles

• Axons may synapse with many other neurons

25 different neurotransmitters

acetyocholine

norepinephrine

NERVE

A bundle of axons

also called nerve fibers

REFLES ARC

• Rapid predictable and involuntary responses to stimuli

PERIPHERAL NERVOUS SYSTEM

• Made up of nerves that lie outside the CNS

• cell bodies (called ganglia) found outside the CNS

• 2 structural types– cranial nerves– spinal nerves

Cranial nerves

• Carry impulses to and from the brain

• 12 pairs

• some are sensory

• some are motor

• some are mixed

Spinal nerves

• Carry impulses to and from spinal cord

• all are mixed

• 31 pairs

Functional classification of PNS

Sensory

• Carries information to CNS from sense organs and sensory receptors

• example: eye, Merkel discs

Motor

• Somatic - allows one to consciously control skeletal muscles

• autonomic nervous system - regulates activity of smooth and cardiac muscles and glands

2 branches of the autonomic nervous system

• Sympathetic nervous system

• parasympathetic nervous system

SYMPATHETIC

• Controls body’s response to emergency situation and stress

• increase blood glucose levels in blood• in heart rate• increases oxygen uptake• decrease activity of digestive system and urine

output• dilates pupils• goosebumps/ perspiration

PARASYMPATHETIC

• Opposite

• normal no stress situations

• steadies heart rate

• constricts pupils

• no effect on sweat glands

CNS

PROTECTION

• Meninges - connective tissue membranes around the brain

• cerebrospinal fluid - cushions,– formed by choroids plexuses,– fluid continually moves through ventricles and

between the brain and spinal cord, – 1/2 cup of fluid

SPINAL CORD

• 17 inches long

• 2 way connection with brain

• ends at lumbar vertebrae #2

• rest of column filled with spinal fluid

• has gray and white matter

• Caudal equina – collection of spinal nerves that extend from the end of the spinal cord

• Paralysis – result of injury to cord

• Severity due to location on spinal cord

GRAY MATTER

• Contains cell bodies and nonmyelinated fibers

• contains portions of sensory and motor neurons

WHITE MATTER

• Myelinated axons of interneurons that run to the brain and from one side of the SC to the other side ( called tracts)

PARTS OF THE BRAIN

http://www.psych.ualberta.ca/~ITL/brain/

Ventricles

• Interconnecting cavities filled with CSF

• 4: 4th, 3rd, and 2 lateral ventricles

Medulla Oblongata

• Regulates heart beat, blood pressure, and breathing,

• Has reflex centers for swallowing, coughing, sneezing, hiccupping and vomiting

• Has nerve tracts between the spinal cord and brain

Pons

• Works with medulla to regulate breathing rate

• Mostly a fiber tract

MIDBRAIN

• Relay station for tracts passing between the cerebrum and the spinal cord or cerebellum

• Has reflex centers for visual, auditory, and tactile responses

• Contains the cerebral peduncles and corpora quadrigemina

CEREBELLUM

• Maintains normal muscle tone, posture, balance

• Ensures that all of the skeletal muscles work together to produce smooth and coordinated movements

• Essential for skills such as playing the piano or hitting a baseball.

hypothalamus

• Forms floor of the 3rd ventricle• Maintains homeostasis by regulating hunger,

sleep, thirst, body temperature and water balance.• Sex, pain , and pleasure centers are located here • Part of the limbic system• Called emotion visceral brain• Regulates the pituitary gland therefore it is the link

between the nervous system and the endocrine system

THALAMUS

• Serves as a relay station for sensory impulses traveling upward to other parts of the brain to the cerebrum

• Involved in arousal and higher mental functions such as memory and emotion

• Gives one a crude awareness of whether the sensation will be pleasant or not

Pineal gland

• Secretes the hormone melatonin

• At night the pineal gland produces melatonin - causes one to fall asleep

LIMBIC SYSTEM

• System of tracts and nuclei

• Surround the brain stem

• Called emotional brain

• Blends higher mental functions and primitive emotions into a whole

• Area that makes eating and sexual behavior seem pleasant

Parts of limbic system

• Hippocampus

• Amygdala

• Thalamus

• Hypothalamus

• Frontal lobe

hippocampus

• Area through which incoming sensory signals generate particular limbic response

• example

Amygdala

• Associated with fear conditioning and associating danger with sensory stimuli

• May be responsible for controlling human aggression

Frontal lobe

• Keeps limbic system in check

• It uses reason to keep us from acting out strong feelings

• Alcohol suppresses the frontal lobe and the limbic system takes over

RETICULAR FORMATION

• Nuclei and fibers that extend the length of the brain stem

• Reticular activating system

• Controls the sleep/wake cycle

• Severe damaged can cause one to be comatose

CEREBRUM

CEREBRUM

• Largest portion of the brain

• Divided into left and right cerebral hemispheres

• Surface has gyri – elevated ridges of tissue

• Sulci – shallow grooves

• Fissures – deeper grooves

• Divided into lobes

• Lobes named after cranial bones

• Gray matter

• Center for association, integration, and learning

CORPUS CALLOSUM

• Bridge of nerve tracts that connect the right and left hemispheres

• Tracts cross – left controlled by right side of brain

• White matter – tracts that carry information from 1 part of cerebrum to another part

• Basal nuclei – relay stations that help to regulate motor activities – islands of gray matter found deep within the white matter

LOBES

• Occipital – vision

• Temporal – hearing

• Frontal - olfactory and higher learning

• Parietal

Functional areas of the cerebral cortex

• Somatic sensory area– Impulses from the body’s sensory receptors,

except for the special senses, are localized and interpreted in this area of the brain

• Primary motor area– Allows us to consciously move our skeletal

muscles

GENERAL INFORMATION

Falling in love

• Pleasure center in the hypothalamus

• Brain neurotransmitters – norepinephrine and dopamine

• They give brain a pleasure flush (cousins of amphetamines)

• Falling in love – pleasure center is bathed with dopamine and norepinephrine

BLOOD BRAIN BARRIER

• Composed of least permeable capillaries in the body

• Prevents urea and most drugs from entering the brain tissue

• Useless against fats, respiratory gases

• Keeps internal environment of brain very controlled

DISEASES/DISORDERS

• Multiple sclerosis• Huntington’s chorea• Parkinson’s disease• Meningitis• Hydrocephalus• Concussion• Contusion• Cerebral edema

• CVA

• TIA

• Alzheimer’s disease

• Quadriplegic

• Paraplegic

• Type A personality

• Cerebral palsy

• Spina

• bifida