Anatomy & Physiology 12 - Nervous System

synapse definition

where neurons communicate with each other

• action potential triggers presynaptic neuron to release neurotransmitters

neurotransmitters definition

chemicals that transmit nerve impulses across synaptic cleft

glial cells (synaptic support)

regulates concentration of neurotransmitters around synaptic cleft

• release ATP which help synaptic function

axon bulb

swollen terminal knobs on ends of axon terminal branches

presynaptic membrane

membrane of axon at synaptic ending

• sends impulse

postsynaptic membrane

dendrite membrane beyond presynaptic membrane

• recieves impulse

synaptic cleft

space between presynaptic and postsynaptic membranes

synaptic vesicles

transport neurotransmitters located near surface of synaptic endings

excitatory neurotransmitters

makes action potential happen (learning, rewards, feeling good)

• glutamate, acetylcholine, noradrenaline, dopamine

inhibitory neurotransmitters

prevents action potential from happening (sleep, fine tune neural processing)

• GABA, glycine, serotonin

action potential requirements

more excitatory neurotransmitters than inhibitory neurotransmitters binding at postsynaptic membrane

5 steps of synaptic transmission

1. contractile proteins pull synaptic vesicles to presynaptic membrane

2. vesicles fuse with presynaptic membrane

3. neurotransmitters released into synaptic cleft through exocytosis

4. neurotransmitters diffuse across synaptic cleft

5. binding of neurotransmitters to specific receptors on postsynaptic membrane, opening ion channels

neurotransmitter deactivation process

neurotransmitter degraded by enzymes

• to prevent neurotransmitters from continuously acting on postsynaptic membrane

ion which begins process of moving synaptic vesicles toward presynaptic membrane

calcium

relation between neurons and electrical signals

neurons generate electrical signals through brief, controlled, changes in permeability of their cell membranes of particular ions

trait in axoplasm which causes negative polarity

large negative anions (organic proteins) in axoplasm

distribution of ions during resting potential of neuron

na/k pump pushes 3 Na+ out for every 2K+ brought in

action potential definition

• electrochemical change that moves in one direction along length of nerve fiber

• changes in ion concentrations cause changes in voltage

cause of action potential

nerve stimulation: sensory stimuli which leads to message being sent to muscle or gland, thought, electric shock, pH change

depolarisation axomembrane actions

• Na+ protein channels open, Na+ moves from outside to inside

• membrane potential changes from -60mV to +40mV

repolarisation axomembrane actions

• Na+ channels close FIRST

• K+ protein channels open SECOND, K+ move from inside to outside

• membrane potential changes from +40mV to -60mV

recovery/refractory period actions

• protein CARRIER transports na/k across membrane

• 3 Na+ go outside, 2 K+ ions go inside, against gradient

order of action potential process

1. resting potential

2. DEpolarisation

3. REpolarisation

4. recovery/refractory period

myelin sheath function in transmission speed

allows rapid speed of nerve impulses to occur

• 200m/s myelinated vs. 0.5m/s non-myelinated nerve fibers

saltatory conduction (myelinated fibers)

nerve impulses jumps from node of ranvier to next node

non-myelinated fibers process

nerve impulse depolarise and repolarise at each point along fiber

neuron functions

1. recieves signals

2. integrate incoming signals to determine if info should be passed along

3. communicates signals to target cells or other neurons, muscles, glands

dendrites function

conducts nerve impulses TOWARD cell body (contains nucleus)

axon function

conducts nerve impulses AWAY from cell body

myelin sheath definition

layer of lipids covering axon

myelin sheath function

prevents electrical signal from decaying due to current leakage through membrane

glial cell in central nervous system

oligodendrocytes

glial cells in peripheral nervous system

schwann cells

glial cell function

form myelin sheath by wrapping their plasma membranes around axon

• supply nutrients, oxygen

• destroys pathogens and remove dead neurons

• insulate one neuron from another

nodes of ranvier definition

gaps between schwann cells of myelin sheath which expose axon

sensory (afferent) neuron function

takes message from receptor in sense organ to CNS

• long dendrites, short axon

interneuron (association/connector neuron)

completely contained within CNS

• conveys messages between sensory/motor neuron

• dendrites/axons may be short or long

motor (efferent) neuron

takes messages from CNS to muscle fiber/gland

• short dendrites, long axon

interneuron relation to reflex

• interneurons located in grey matter of spinal cord

• interneurons connects sensory to motor neurons in reflex arc

• reflex automatic because reflex arc faster than message travelling up spinal cord to cerebrum

  • ex. pulling hand away from stove before screaming

exteroceptor

located near a stimulus in EXTERNAL environment

• ex. receptors located in skin

interoceptor

interprets stimuli from INTERNAL organs and tissues

• ex. receptors that sense blood pressure in aorta

proprioceptor

located near moving part of body, interprets positions of tissues as they move

• ex. muscle, joint capsule

macromolecules relation to transmembrane receptor proteins

macromolecules affect the transmembrane receptor proteins by binding or directly diffusing across the cell membrane

chemoreceptor

detect chemical stimuli

• ex. chemicals that lead to sense of smell

osmoreceptors

respond to solute concentration of body fluids

nociceptors

detect pain, interpret presence of chemicals from tissue damage

mechanoreceptors

detect physical stimuli

• pressure, vibration, sensation of sound, balance

2 ways receptors are categorised by

1. location relative to stimuli

2. type of stimuli they transduce (convert from a form of energy to electrical energy)

central nervous system

spinal cord and brain

peripheral nervous system

all nerves connected to spinal cord

somatic nervous system

nerves connected to skeletal muscles (voluntary and reflexes)

autonomic nervous system

nerves connected to smooth and cardiac muscles as well as glands (involuntary)

sympathetic nervous system

effects associated with emergency situations

parasympathetic nervous system

effects associated with normal state

central nervous system function

sensory information recieved, motor control initiated

cerebrospinal fluid location and function

located between membrane and CNS for cushioning/protection

medulla oblongata function

regulate/ensure primitive functions

• controls heart rate, breathing, blood pressure, coughing, sneezing, vomiting, hiccups, swallowing

pons function

works with/connects medulla oblongata to cerebellum/cerebrum

hypothalamus

complex regulatory functions

• maintains homeostasis

• regulates hunger, sleep, thirst, water balance, body termp, blood pressure, sexual response, fight or flight response

pituitary gland function

controlled by hypothalamus, secretes hormones into blood (connects nervous/endocrine/circulatory systems)

thalamus

• recieves sensory impulses from all parts of body EXCEPT FOR SMELL

• channels impulses from spinal cord and lower brain to cerebrum to interpret

cerebellum

• controls complex muscular movement

• makes sure skeletal muscles work together smoothly

• responsible for maintaining normal muscle tone, posture, balance

cerebrum

• lots of folds to integrate info from thalamus

• controls balance via reception of sensory information from inner ear

• only place where consciousness resides, intellect/learnng, memory

basal ganglia

specialised nerve cells under cerebrum

• associated with control of voluntary motor moves, procedural learning, routine behaviours/habits, eye movements, cognition

cerebral hemispheres

• left and right side of brain

• each contain 4 lobes that gather sensory information

corpus callosum

piece that connects cerebral hemispheres horizontally, transmitting information between them

frontal lobe

movement, problem solving, concentration, planning

parietal lobe

sensations: touch, temp, pressure, pain, taste

temporal lobe

hearing, smelling, memory of visual scenes, music, complex sensory patterns, understanding speech, using words

occipital lobe

vision, combining visual experiences with other sensory experiences

spinal cord

extends from base of brain to vertebral canal

• contains grey matter (integrate message)

• white matter (carries messages)

ganglia

collections of nerve cell bodies

dorsal root ganglion

enters grey matter of spinal cord

central root ganglion

exits grey matter of spinal cord

sympathetic fight or flight response symptoms

• pupils dilate

• less energy for digestion, less salivation

• increase heart rate, breathing rate, perspiration

neurotransmitter in sympathetic nervous system

noradrenalin, increases heart rate during fight or flight response

nerve fibers in sympathetic nervous system

arise from middle of spinal cord

• short ganglionic fiber

• long postganglionic fiber

parasympathetic nervous system response symptoms

• pupils contract

• more energy for digestion

• LESS heart rate, breathing rate, perspiration

parasympathetic nervous system neurotransmitter

acetylcholine

parasympathetic nerve fibers

• arise from upper/lower part of spinal cord

• long preganglionic fiber

• short postganglionic fiber