the nervous system Flashcards
nervous system consists of
spinal cord. brain, and all peripheral nerves
primary functions of CNS
1) sensory input
2) interpretation
3) motor output
sensory input
detect changes to body’s internal and external environment = stimuli
also known as afferent nerves
interpretation
sensory input converted into electrical signals called ‘nervous impulses’ that are transmitted back to brain. here the signals are consolidated to created sensations, thoughts, decisions and even memories.
motor output
nervous system responds stimuli by sending signals to muscles and/or glands. instruct the muscle or gland to increase or decrease activity. signals which produce movement are called ‘motor signals’ or ‘efferents’
PNS (Peripheral Nervous System)
31 pairs of nerves outside spinal cord and brain
branch off spinal cord through tiny holes in vertebrae called ‘foramen’
junction at which one nerve joins another is referred to as a ‘synapse’
PNS can be further can be divided further into the
Somatic Nervous System
Autonomic Nervous System
Somatic Nervous System
- Primarily associated with efferent or motor activity
- Largely responsible for controlling voluntary activity
- The nerves that form the somatic nervous system are called ‘motor neurons’
- Under conscious control but does rely on sensory feedback from external sensory receptors
- These receptors are:
- Nociceptors = pain stimulus
- Thermoreceptors = heat/temperature stimulus
- Mechanoreceptors = touch, feel, pressure stimulus
- Proprioceptors = motion, position and tension stimulus
autonomic nervous system
- Primarily concerned with involuntary processes
- Regulates hormone secretion from glands
- Controls organ activity
- Regulates HR and blood pressure
- Controls body temperature
- Regulates digestion
- Contracts/relaxes smooth and cardiac muscle
- This system relies on feedback from internal sensory organs
- These organs are:
- Baroreceptors = pressure within organs and vessels
- Osmoreceptors = concentration of water in blood
- Chemoreceptors = concentration of gasses in blood
- Proprioceptors = pressure and deformation in muscle-reflexes only
- Thermoreceptors = temperature of internal environment
sympathetic and parasympathetic
autonomic system can be further divided into sympathetic and parasympathetic systems
sympathetic division
generally sends stimulatory impulses to target organs in an attempt to speed them up
for eg, during exercise the heart receives sympathetic stimulation from autonomic nervous system to increase rate at which it contracts
parasympathetic sub-system
typically concerned with inhibitory actions to reduce activity of the target organ
eg, arteries supplying the active tissues during exercise receive a parasympathetic stimulation which causes their smooth muscle lining to relax, thus enabling them to stretch, or dilate, under increased pressure
neurotransmitters
nerves communicate by releasing chemical messengers called neurotransmitters
they diffuse across nerve junction/synapses to stimulate next nerve or cell
electrical signals travel along the length of a nerve until they reach the synapse. this is where neurotransmitters are released and signal becomes chemical.
when neurotransmitters reach post synaptic membrane of nerve, it becomes electrical again.
some common neurotransmitters
acetylcholine - muscle cell communication
dopamine - brain cell communication
adrenaline - varied roles throughout the body
noradrenaline - varied roles throughout the body
parasympathetic nerves within the autonomic nervous system are entirely responsible for
suppressive and inhibitory activities like slowing heart rate, relaxing smooth muscle tissue and reducing glandular activity
parasympathetic nerves within the autonomic nervous systems release
the neurotransmitter ‘acetylcholine’ from their terminal end.
this neurotransmitter is therefore used to suppress and inhibit the activity of the target organs/cells
also in some systems, acetylcholine is used to excite cells
baroreceptors
tiny pressure receptors located inside larger arteries, including aorta, which provide feedback to CNS about changes in arterial pressure.
so, when HR increases so does the arterial blood volume, which then causes blood pressure to rise. this pressure is detected by baroreceptors and fed back to the CNS.
baroreceptors and parasympathetic response
when a pressure increase is detected by the baroreceptors and fed back to the CNS, it exerts a parasympathetic response on the arteries supplying the active tissues. causes them to relax and widen.
vasodilation
large volume of elastin within the artery wall means artery is able to stretch or dilate
it is a passive stretching response that occurs because of the increased pressure
vasoconstriction
simultaneously to parasympathetic response, a sympathetic response is exerted on arteries supplying the non-active tissue, which cause them to narrow or constrict.
vasoconstriction excites the smooth muscle tissue that lines the arterial wall and causes immediate reduction in the diameter of the arteries lumen; this narrowing process reduces blood flow and diverts it to the dilated arteries where it is needed.
primary purpose of both vasodilation and vasoconstriction
to divert more blood towards the active tissues.
components of a neuron
cell body dendrites axon nodes of ranvier myelin sheath terminal end
cell body
this is the brain of the cell and contains both the nucleus and DNA. regulates all cell activity
dendrites
tree-like structures that receive information from the terminal end of adjacent nerves.
the dendrites relay this information to the cell body, which is subsequently interpreted and transmitted along the axon towards the terminal end.
axon
the elongated fibre that transmits information away from the cell body towards terminal end.
nodes of ranvier
these are the non-insulated spaces along the nerve’s axon, which allow electrical signals to rapidly jump from one myelin to the next, thus speeding up the rate at which impulses travel along the nerve. this process is known as depolarisation an repolarisation.
the nodes of ranvier, which expose the axon, also allow nutrients and waste products to enter the nerve cells.
myelin sheath
myelin is the fatty sheath that provides the protective and insulating case surrounding the nerve’s axon; the myelin sheath enables impulses to travel along the nerve at lightening speeds and with little resistance
terminal end
sometimes called and ‘axon terminal’ or ‘synaptic terminal’, the terminal end contains an extensive range of sacs (vesicles) that store and release a variety of neurotransmitters essential for nerve function.