Nervous system Flashcards
explain the conduction of a nerve impulse along myelinated fibres
- depolarisation occurs
- saltatory conduction at nodes of Ranvier
- cell membrane becomes permeable to sodium ions
- needs to reach theshold (-55mV)
- sodium ions inter the cell
- membrane becomes positive to outside
- potassium ions diffuse out
- hyperpolarisation
- sodium-potassium pump acts: sodium out and potassium in
- membrane returns to polarised state
- action potential triggers depolarsiation in adjacent membrane regions
explain the transmission of a nerve impulse across a synapse
- When action potential reaches the axon terminals it triggers calcium gates, causing calcium to flood into the axon terminal
- The calcium binds with vesicles containing neurotransmitters and allows them to move to the cell membrane, releasing the neurotransmitter into the synaptic cleft
- These neurotransmitters diffuse across the synaptic cleft and attach to receptors on the membrane of the next neuron (dendrites/post-synaptic membrane)
- Results in the initiation of an action potential in the post-synaptic neuron (sodium gates open into the dendrites)
how do neurotransmitters go away after transmission across a synapse
Diffusion
Re-uptake (back into the axon terminal to be used again)
Broken down
how is the nervous system protected
bone
meninges
cerebrospinal fluid
explain how bone protects the nervous system
Cranium protects brain, vertebral column protects spinal cord
Protects from physical injury
explain how meninges protects the nervous system
Holds brain and spinal cord in place, carry blood vessels to the brain
Inner layer: dura mater
- tough and fibrous
- sticks closely to cranium/vertebral canal
- anchors CNS to bone
Middle layer: arachnoid mater
- loose mesh of fibres
- connects with inner layer
Outer layer: pia mater is delicate
- contains many blood vessels
- sticks closely to the surface of brain and spinal cord
explain how cerebrospinal fluid protects the nervous system
Supports brain, gives it a medium to float in
shock absorber - protects from mechanical injury
Occupies space between meningeal layers
Circulates through 4 cavities in the brain and centre of spinal cord
Clear watery fluid containing cells, glucose, proteins, urea and salts
Formed from blood, circulates through CNS and takes nutrients to neurons and removes wastes and eventually returns to capillaries
give examples of neurotransmitters
acetylcholine
adrenaline
dopamine
histamine
list other functions of the cerebrospinal fluid
Shock absorber, protects from mechanical injury
Delivers nutrients to cells of CNS
Removes wastes
Regulates concentration of H+ and CO2, which regulates breathing
Maintains fluid to bathe cells of the brain
Transport chemical messengers around CNS
what are the 2 parts to the cerebrum
cerebral cortex
basal ganglia
describe the structure of the cerebral cortex
outer surface of cerebrum, grey matter - 2-4mm thick
folded - rounded ridges called convolutions, shallow downfolds calls sulci, deep downfolds called fissures
longitudinal fissures separate cerebral cortex into 2 cerebral hemispheres
hemispheres have four lobes: frontal, parietal, temporal, occipital
joining the hemispheres at the base of the longitudinal fissure is the corpus callosum (area of white matter)
what is the function of the cerebral cortex
involved in thinking, reasoning, learning, memory, intelligence, sense and responsibility
3 basic functions:
sensory areas: interpret impulses
motor areas: control muscular movement
association areas: intellectual and emotional processing
explain the structure of the basal ganglia
grey matter below cerebral cortex
composed of tracts - bundles of nerve fibres
mostly unmyelinated axons
outside of CNS
what is the function(s) of the basal ganglia
regulates muscle tone
integrates complex muscles actions in complicated, learned ways (e.g. walking)
what is the function of the cerebellum
takes place below conscious
receives information from inner ear and stretch receptors in skeletal cells
controls posture, balance and fine coordination of voluntary muscles
damaged cerebellum - jerky, uncontrolled movement
describe the structure of the cerebellum
2 hemispheres
surface is folded into parallel ridges
outer folded part of grey matter
inside is white matter that branches to all parts of the cerebellum
list some functions of the hypothalamus
regulates body temperature
regulates autonomic nervous system: heart rate, blood pressure
regulates food and water intake
secretion of hormones
what 3 components is the brain stem composed of
medulla oblongata
pons
midbrain
what is the role of the medulla oblongata
important role in automatically adjusting body functions
regulates swallowing, sneezing, coughing, vomiting
contains 3 centres:
- cardiac: rate and force of heartbeat
- respiratory: rate and depth of breathing
- vasomotor: diameter of blood vessels
INFLUENCES BY HYPOTHALAMUS AND OTHER HIGHER CENTRES OF THE BRAIN
explain the functions of the spinal cord
carry sensory impulses to the brain and motor impulses away from the brain
integrate certain reflexes.
list some changes that the autonomic nervous system causes
heart rate
blood pressure
digestion
pupil diameter
what is meant by a fight or flight response
In threatening situations the balance between sympathetic and parasympathetic stimulation is upset and the sympathetic becomes dominant
Situations that involve fear-anger, stress, danger or competition provoke what is called a fight-or-flight response or alarm reaction
These responses prepare the body for increased activity
activation of sympathetic nervous system include:
- increase heart rate and force of contraction
- dilation of blood vessels in neccessary organs: liver,
heart, skeletal muscles
- dilation of airways in the lungs and increased depth and
rate of breathing
what are ‘receptors’
Structures within the cell membrane that are capable to detect a change in the body’s internal or external environments
list some different types of receptors
osmoreceptors
chemoreceptors
touch receptors
pain receptors
thermoreceptors
explain what an osmoreceptor is
detect osmotic pressure/water balance. Located in the hypothalamus
explain what an chemoreceptor is
detect specific chemicals
Detect smell and taste in the nose and mouth
Detect oxygen, carbon dioxide and pH in blood vessels, and are involved in the regulation of heartbeat and breathing rate
explain what an thermoreceptor is
detect heat and cold
In skin – detect external temperatures
In hypothalamus – detect internal body temperature
what is a reflex
Rapid, automatic response to a change in the external or internal environment
mostly coordinated by spinal cord
The impulse may be passed to motor neurons at the same level in the cord, or may travel a few segments up or down the cord before travelling out through a motor neuron
In these cases the reflex is carried out by the spinal cord and is known as a spinal reflex
what are the 4 properties of reflexes
A stimulus is required
Involuntary
Rapid response
Stereotyped
what is a reflex arc
The pathway a nerve impulse follows in travelling from a receptor to an effector
or in the case of a spinal reflex, a spinal reflex arc
what are the components (what happens) in a reflex arc
The receptor reacts to a change in the internal or external environment by initiating a nerve impulse in the sensory neuron.
A sensory neuron carries impulses from the receptor to the CNS
There is at least one synapse. The nerve impulse may be passed directly to a motor neuron or there may be one or more interneurons
A motor neuron carries the nerve impulse to an effector – away from CNS
An effector receives the nerve impulse and carries out the appropriate response. Effectors are muscle cells or excretory cells.
what are learned reflexes
More complex motor patterns appear during a baby’s development – e.g. sucking, chewing, following movement with eyes
These innate reflexes are determined genetically
Some complex motor patterns are learned and are called acquired reflexes
They are learned through constant repetition
what is the difference between the somatic and autonomic nervous system
SOMATIC:
- carries message to skeletal muscles
- neurotransmitter used is acetylcholine
- one nerve fibre from CNS to effectors - no ganglion and synapse
- voluntary
AUTONOMIC:
- carries messages to involuntary muscles and glands
- neurotransmitter used is acetylcholine or noradrenline
- 2 nerve fibres from CNS to effector - with a synapse in a ganglion
- involuntary
