Peripheral nerves Flashcards
Functions of the nervous system- communication and homeostasis
master controlling and communicating system of the body, monitors the bodys internal and external environment via afferent sensory input, integrates sensory input and motor commands
Functions of the nervous system- responses
coordinates involuntary and voluntary responses of many other organ systems via efferent motor output
Sensory receptors
sensory receptors in skin, joint muscle- sensory input, sends information via peripheral nerves to the brain and spinal cord- the information is integrated and processed, this stimulates a motor output in the muscular system
central nervous system
brain- receives and processes sensory information, initiates responses, stores, memories generate thoughts and emotions, spinal cord- conduct signals to and from the brain, connects reflex activities
Peripheral nervous system
motor neurone- CNS to muscle gland, sensory neurones- sensory organs to CNS, 2 motor neurones- somatic nervous system- controls voluntary movement, autonomic nervous system- controls involuntary response, 2 autonomic NS- sympathetic (fight and flight), parasympathetic (rest and digest)
what is the lower motor neurone
neurons with cell bodies in spinal cord or brainstem whose axons directly innervate skeletal muscle- peripheral nerves
what is the upper motor neurone
neurons that transmit information from the brain to lower motor neurons and the interneurons in the brainstem and spinal cord- central nerves
Peripheral nervous system- cranial nerves
carrying information to and from the brain, e.g. vagus nerve 10- controls heart and lungs, and facial nerve 7- this supplies the muscle of the face- problems can result in dropping of the face
Peripheral nervous system- spinal nerves
carrying information to and from the spinal cord
Peripheral nervous system
they have the ability to amend themselves, whereas nerves in the CNS cannot repair, 31 peripheral nerves
Autonomic nervous system
unconscious- sympathetic NS, and parasympathetic NS
Sympathetic NS
emerge from the thoracic or lumbar region of the spine- can lead to increased blood pressure (flight or fight)
Parasympathetic NS
emerges from cranial and sacral parts of the spinal cord- damage to this nervous system slows everything down, e.g. heart rate
Peripheral nerves
they come into the spinal cord, via ascending tracks- to the brain, lots of dorsal columns bring info up spinal cord to the brain
lateral spinal cord- brings info down the brain
sensory info goes into the back of brain, motor information goes out the front
layers of peripheral nerves
epineurium, perineurium, endoneurium, then a small nerve cells
what are all spinal nerves
mixed nerve- carries both sensory (afferent) and motor (efferent) fibres
basic neuron types
bipolar- interneuron
unipolar- sensory neuron
multipolar motor neuron
basic nerve structure
dendrites- bring ingo into the cell body, cell body- has a nucleus and mitochondria, axon- to another nerve or muscle, to synaptic cleft
What does the CNS have- astrocytes, microglia and oligodendrocytes
astrocytes- link cells together and form structure, microglia- additional immune cells that are placed within the brain, oligodendrocytes- these cover nerves in CNS, they provide protection
what does the PNS have
schwann cells- wrap themselves around peripheral nerve and provide covering, they have a neurolemma, this provides structures for regeneration
what do dendrites transmit
they transmit an electrical impulse via chemicals (action potentials) to the cell body
what do the cell body produce
the cell body produces an electrical impulse via chemicals (action potential) which is transmitted down the axon
what do neurotransmitters do
at the end of the axon neurotransmitters are released to transmit the impulse from one nerve to the next or to muscle fibres
what are nerve cells
nerve cells are excitable cells, neurones have a negative resting membrane potential (-70mv), the presence of a membrane potential is called polarisation
how are action potentials started
neuron cell membranes contain ion channels to allow ions into or out the cell, dendrites initiate action potential- stimulate cell body,
what is the state of the cell at resting potential
resting potential- lots of sodium ions on the outside, few potassium ions on the inside- much more negative inside, as action potential starts the sodium channels open and sodium ions go into cell
nerve impulses- 1
stimuli causes Na+ ion channels open, Na+ ions rush into the cell, depolarisation occurs- more positive action potential
nerve impulses- 2
equilibrium is reached, Na channels close- less sodium moving into cell, potassium moves outside the cell, start to see more negative
nerve impulses- 3
K+ channels open- K continues to move out of the cell, repolarization occurs, k channels slowly close, hyperpolarization occur- where it is even more negative on the inside, K and Na pumped out to reach resting potential
Action potential
resting membrane potential- change difference at rest, Na+ is kept relatively high outside vs inside, K+ is kept high inside and outside,
what restores after action potentials
Na+ and K+ pumps restore after action potentials
what is the all or nothing law
changes in resting membrane potential build up to threshold, when the threshold is reached a spike occurs, spike due to Na+ flooding in, once the AP starts, it opens adjacent Na+ gates without fail
what is spatial summation
AP can occur if many short signals arrive at multiple dendrites simultaneously
temporal summation
AP can occur if a series of signals arrive at one synapse
what is continuous conduction
can happen in myelinated- bigger and transfer info quicker, and non- myelinated nerves- smaller not as quick,
what is saltatory conduction
occurs in myelinated nerves- saltatory conduction- impulse jumps between axons= quicker
what are chemical synapses
presynaptic cell releases, act on postsynaptic cell (help initiate AP) they release neurotransmitters
what do neurotransmitters excite or inhibit
they can excite or inhibit- calcium needed to open neurotransmitter gates
examples of neurotransmitters- acetylcholine and serotonin
Ach- muscle contraction
serotonin- responsible for depression
examples of neurotransmitters- dopamine, norepinephrine, Gaba
dopamine- lack of dopamine causes parkinson’s, too much dopamine can lead to schizophrenia, GABA
damage to neurones
neurons have little regeneration capacity, CNS- no ability to repair damage
PNS damage
myelinated cells are able to repair (neurolemma), only if cell body and schwann cells are intact,
PNS degeneration
chromatolysis- occurs shortly after axon damage, wallerian degeneration- distal portion degrades
axon regeneration
intact neurolemma cells divide, formation of regeneration tube, new axon will reform
re-myelination
eventually, myelin reforms
types of peripheral nerve injuries- transient ischemia
lack of oxygen to area supplied by nerve, caused by compression
types of peripheral nerve injuries- neurapraxia
next level of nerve damage, ad a result compression, will regenerate but will take 6-8 weeks
types of peripheral nerve injuries- axonotmesis
axon is damaged not completely served, can be caused by a pulling injury or crushing/ compression of nerve, endoneurium and perineurium are intact, regeneration can occur
types of peripheral nerve injuries- neurotemiss
complete severance of nerve- can be sewed back together- as long as right things are sewed together- can regenerate
