The Nervous System Flashcards
What are the roles of the nervous system?
-sensory: to sense changes within the body and the outside environment
-integration: to interpret the changes
-homeostasis: initiating changes in the form of muscular contractions, glandular secretions and through motor movement
what makes up the CNS and what does it do?
the brain and the spinal chord, acts as a control centre and associates inputs with outputs
what makes up the PNS and what does it do?
made up of neurones and nerves that connect the CNS with receptors and effectors
-carries info from receptors and carries instructions to effectors
how is the brain protected?
-bone being the skull
-CSF for cushioning
-highly selective blood brain barrier
-mininges
what are the three layers of meninges?
-pia mater: thin, highly vascular and closely adhering
-arachnoid: delicate web like, transparent
-dura mater: tough and fibrous outermost layer
What are the cells in the CNS and give some features of these as a whole
Glial cells which consist of astrocytes, microglia and oligodendrocytes and they:
-make up 90% of the cells in the CNS
-do not initiate / conduct nerve impulses
-communicate with neurones and each other
-support neurones physically and metabolically
- homeostatically control the specialised extracellular environment for optimal neurone function
what are the functions of astrocytes?
-provide neurones with physical support as they act like a glue and hold them together
-act as scaffolding during foetal development
-neural scar formation
-absorb and degrade some of the neurotransmitters that are released in their area and so brings their actions to a stop
-nutrient transfer to neurones from the blood
-aid in the maintenance of optimal ions for neurone excitability
-provide chemical communication with neurones and each other via gap junctions/ glutamate receptors
what are the five sections of the spinal cord in their categorised limb?
fore limb: cervical nerves, thoracic nerves
hind limb: lumbar nerve, sacral nerve and the coccygeal nerve
be able to label the white and gray matter parts of the spinal cord
give the functional organisation of the spinal chord
-the dorsal horn where cell bodies of interneurons on which afferent neurones terminate
-the lateral horn which is the cell bodies of autonomic efferent nerve fibres
-ventral horn which is cell bodies of somatic efferent neurones
what is white matter and whats its two functions?
bundles of nerve fibres
-ascending tracts (SC to brain) transmit afferent input signals to the brain
-descending tracts (brain to SC) relays brain messages to effernet neurones
what perforates the dura mater?
the 12 cranial nerves of the brain
What nerves make up the PNS?
31 pairs of spinal nerves and 12 pairs of cranial nerves
what is the only cranial nerve that doesnt go to the head and neck?
the vagus nerve
why is there progressive nerve branching in the PNS?
-provides network of peripheral nerves
-allows supply to a particular/ specific regions of the body
give the sequence of organisation of the nervous system
- afferent division
- input to CNS from periphery goes to brain and spinal cord
3.output from CNS to periphery - efferent division
- transferred to either skeletal muscle or smooth muscle, cardiac muscle, exocrine glands or some endocrine glands
what division for:
cns to internal environment
internal environment to CNS
CNS to external environment
external environment to CNS
efferent
affernet
efferent
afferent
what is the functions of the afferent division of the CNS?
-detects, encodes and transmits peripheral signals to the CNS for processing
-have specialised neurone endings to detect changes in the internal and external environment
what are the two different types of afferents?
-visceral afferents= carry subconscious info from internal viscera
-sensory afferents = carry conscious/ sensory info
what are the 5 types of sensory receptor?
-photoreceptors: light
-mechanoreceptors: touch, stretch, pressure, hearing and balance
-thermoreceptors: temp,
-chemoreceptors: taste smell
-nociceptors: tissue damage, pain related
what is the pathway of an impulse from stimulus to CNS
stimulus
receptor - sensory transduction
receptor potential - graded potential
afferent neuron
action potential
CNS
what are the two divisions of the efferent division of the PNS and what do they divide into?
-somatic nervous system -> motor neurones -> skeletal muscles
-autonomic nervous system -> sympathetic and parasymathetic -> smooth muscle, cardiac muscle, exocrine and some endocrine glands
describe the 2 neurone chain of the autonomic NS
preganglionic neurone synapses with ganglion of the postganglionic neurone that innervates the visceral effector being smooth muscle, cardiac muscle and glandular epithelia
summarise the structure of the sympathetic division of the autonomic NS
-forms thoracolumbar outflow
-ganglia are close to the CNS
-short preganglionic fibres
-long postganglionic fibres
summarise the structure of the parasympathetic division of the autonomic NS compared to the sympathetic
-forms craniosacral outflow
-the ganglia are near the effectors
-long preganglionic fibres
-short postganglionic fibres
what are the other words for noradrenaline and adrenalin?
norepinephrine and epinephrine
What is the motor end plate?
a specialised groove in the muscle cell membrane into which the axon terminal button fits
give the pathway to the initiation of muscle contraction
the AP reaches termini
-voltage gated Ca2+ channels open
-Ca2+ diffuses into the axon terminal button
-ACh releases into the cleft
-ach binds specific receptor channels on MEP
-channels open so Na+ IN and K+ OUT
where is the spinal chord located?
between brain and afferent &efferent nerve fibres of the PNS
what are the two primary functions of the spinal chord?
-transmission of info between brain and rest of body
-integration of reflex activity between afferent and efferent output without brain involvement
what are the two types of reflex?
simple basic
acquired conditioned reflex
why are most reflexes polysynaptic?
-as a result of interneurons being present
How are spinal reflexes and the somatic NS related?
-the motor reaction signals the input triggering the involuntary movements involving sense organs and effectors
-the inputs are received from peripheral sensory receptors so muscles, joints and skin
the effector organs are voluntary striated skeletal muscles
give the reflex arc pathway
1.sensory receptor
2. afferent nerve fibres
3. integrating centre: SC and brain stem (basic) higher brain levels (aquired)
4. effernet nerve fibres
5. effectors
what is the stretch reflex for? what does is occur in response to?
the maintenance of erect body posture
muscle stretch
why is the stretch reflex monosynaptic
its only made of 2 neurones
how does the stretch reflex work?
- triggered by muscle stretch - muscle spindle detects change in muscle length and negative feedback ensures optimal resting length
- sends impulse to sensory neurone
- gets taken to spinal cord which synapses with efferent neurone
4.this takes the response back to the muscle
what and where are the muscle spindles?
collection of intrafusal fibres within a spindle shaped CT capsule and lie parallel to the extrafusal muscle fibres
what are the two types of afferent neurones in muscle spindle and what do they do?
-Ia neurones (centre) detect changes in fibre length and speed
-II neurones (ends of the spindle) detect changes in length
what are the two types of efferent neurones in muscle stretch and what do they do?
gamma motor neuron - terminate on the intrafusal fibres
alpha motor neurone - terminate on the extrafusal fibres
what’s the role of spindles in the stretch reflex?
-muscle spindles stretch when the muscles are activated
-la sensory axon sends an action potential which triggers alpha motor neurone activation to contract the muscle
-spindle begins to relax and la sensory axon stops firing
-co activation of the gamma motor neurone contracts end regions of intrafusal fibres of the muscle spindle
-slack of the spindle reduces
-la sensory axon is triggered again
how does the arm stretch reflex work?
- weight is added to the muscle
- transient elongation of the muscle
- 1a afferent neurone has an high frequency of action potential which then reduces
- alpha motor neurone discharge decreases so muscle shortens and the length is maintained by the neurone discharge
how does the patellar stretch reflex work?
-tapping on the patellar ligament stretches
-quadriceps femoris is stretched
-muscle spindles are activated which fires the afferent axons
- impulse travels to spinal cord
-excites ventral quadriceps motor neurone
-ach is released at motor end plate in the NJ
-quads contract
-pulls of patellar tendon, patellar ligament and tibia
give an example of a polysynaptic reflex
the withdrawal reflex
give the pathway of the withdrawal reflex
-thermal pain receptor is activated
-action potential in afferent neurone is generated so impulse is carried to SC
-synsapses with interneorne which is activated and releases an excitatory signal
-motor neurons are stimulated innervating biceps (flexor muscle) so they coontract
-hand is withdrawn from the stimulus
at the same time in the sc the inhibitory interneurone inhibits the motorneurone to the triceps which are extensor muscles so the triceps relax
give the pathway of the flexor withdrawal reflex
-pain stimulus activates the pain receptor
-sends signals via afferent pathway to the SC
-instructions are sent via efferent pathway
-this stimulates the flexor muscle to contract and inhibit extensor muscles
-knee flexes and the foot is withdrawn from pain
how do you not fall over in the flexor withdrawal reflex?
due to the crossed extensor reflex
ensures other leg can bear the weight of the body and the leg is withdrawn
how does the crossed extensor reflex work?
-activation of pathways that cross to the opposite side of the sc
-extensor muscles contract so knee extends
-inhibitory signal to flexor muscles
flexor relaxes
-leg supports the body
how does the brain modify reflexes?
by sending impulses via the descending pathways to efferent motor neurons that supply effector muscles
