Nervous System Flashcards
Functions of Myelin Sheath
insulation, protection and impulse speed increaser
Neurilemma
layer that helps in the repair of injured nerve fibres, wrapped around the Schwann cells
Neuromuscular Junction
‘synapse’ between an axon and a skeletal muscle cell.
Functional Neuron types
Sensory - carry nerve impulses from receptors in sense organs or skin into CNS
Motor - carry nerve impulses from CNS to effectors (muscles and glands)
Interneuron - carry nerve impulses between sensory and motor neurons
Structural Neuron types
Multipolar - 1 axon, multiple dendrites, includes most interneurons and motor neurons
Bipolar - 1 axon, 1 dendrite (both may have branches at ends), occur in eye, ear and nose taking impulses from receptors to other neurons
Unipolar - 1 axon (not found in humans)
Pseudounipolar - 1 axon that splits into two extensions (one end with dendrites and the other with dendrites), includes most sensory neurons
Neuron
nerve cell
Nerve fibre
any long extension of cytoplasm of a nerve cell body - though it usually refers to the axon
Nerve
bundle of nerve fibres held together by connective tissue. called tracts within the CNS, nerves outside it
Extracellular fluid contains?
high concentration of sodium ions (10x higher outside than in). sodium diffusion = limited due to low number of sodium leakage channels
Intracellular fluid contains?
low concentration of sodium ions, but contains potassium ions (30x higher inside than out). potassium diffusion = easy due to high number of potassium leakage channels
Resting Membrane Potential value
around -70mV (i.e. potential inside is 70mv less than outside; it is polarised)
RMP cause
differences in the distribution of sodium and potassium ions (extracellular fluid = more positive than intracellular)
Sodium-potassium pump
carrier protein which moves 2 potassium ions in for every 3 sodium ions removed, i.e. causing a net reduction of positive ions into the cell. against concentration gradient, therefore is active transport and requires ATP
Action potential definition
rapid depolarisation and repolarisation of the membrane caused by opening and closing of voltage-gated channels
Depolarisation (AP)
sudden increase in membrane potential if level of stimulation exceeds 15mV. some sodium channels are opened (ligand- or mechanical-gated) and sodium ions move into cell. if stimulus is strong enough to increase MP to -55mV, voltage-gated sodium channels open, allowing for independent movement of sodium ions into the cell (all or none response). MP reaches +40mV.
Repolarisation (AP)
soon after depolarisation, sodium channels close and voltage-gated potassium channels open, increasing flow of them out of cell. MP decreases again back to -70mV.
Hyperpolarisation (AP)
after repolarisation, potassium channels remain open for longer than is needed; MP decreases further than RMP.
Refractory Period
once sodium channels are opened, they are quickly inactivated (i.e. unresponsive to stimulus)
Transmission of Nerve Impulse
depolarisation of one area causes movement of sodium ions into adjacent areas. this stimulates the opening of voltage gated sodium channels in next part of membrane, initiating a new action potential in said part.
Saltatory Conduction
Because ions cannot diffuse in myelinated areas, they simply jump from one node of Ranvier to the next. this allows myelinated fibres to carry nerve impulses faster than unmyelinated ones
Transmission across Synapse
- nerve impulse activates voltage gated calcium ion channels
- calcium ions flow into the cell at the pre-synaptic axon terminal
- synaptic vesicles resultantly fuse with the membrane, releasing neurotransmitters by exocytosis
- neurotransmitters diffuse across synaptic cleft and attach to receptors.
- this stimulates ligand-gated protein channels to open which allow for the influx of sodium ions, initiating a new action potential in the post-synaptic membrane.
Thermoreceptors
responsive to heat and cold, occurring mainly in the skin.
Osmoreceptors
responsive to the concentration of substances dissolved in the water of the blood plasma. located in the hypothalamus.
Chemoreceptors
responsive to particular chemicals. present in the nose - odours, present in the mouth - tastes, present internally - composition of bodily fluids, present in blood vessels - pH of blood and gas concentrations
Touch receptors
responsive to changes in pressure and vibrations, or simply movements of hairs. found mainly in the skin.
Pain receptors
responsive to damage to tissues, poor blood flow to tissues, or excessive stimulation of things like chemicals or heat. heavily concentrated in the skin and mucous membranes, most organs except for the brain.
Reflex properties
rapid, stereotyped, triggered by stimuli and involuntary
Protection of the CNS
cranium, the meninges and cerebrospinal fluid
Meninges
layers of connective tissues covering the surface of brain and spinal cord
dura mater of meninges
outer layer, tough and fibrous (sticks close to cranium but not so much in vertebral canal)
arachnoid mater of meninges
middle layer, loose mesh of fibres
pia mater of meninges
inner layer, more delicate and contains many blood vessels
cerebrospinal fluid
clear, watery fluid containing a few cells aswell as urea, glucose, protein and salts. it acts as a shock absorber, it suspends the brain and provides nutrients/ gets rid of wastes
Cerebrum
cerebral cortex: thinking, reasoning, learning, memory, intelligence and sense of responsibility, perception of senses and initiation and control of voluntary muscle contraction
sensory areas interpret impulses from receptors, motor areas control muscular movements and association areas are concerned with intellectual and emotional processes
basal ganglia
grey matter deep inside the cerebrum, play a role in initiating desired movements and inhibiting unwanted ones.
frontal lobe
thinking, problem solving, emotion, personality, language, control of movement
parietal lobe
processing temperature, touch, taste pain and movement
temporal lobe
processing memories and linking them with senses, receives auditory information
occipital lobe
vision
insula
recognition of different senses and emotions, addiction and psychiatric disorders
corpus callosum
joins left and right hemispheres of the brain allowing for communication between them
cerebellum
under rear part of cerebrum, controls posture, balance, fine coordination of voluntary muscle movement.
hypothalamus
control homeostasis and many bodily activities, including blood pressure and heart rate, body temperature, contraction of bladder, sleeping, food and water intake, endocrine system, emotion
medulla oblongata
continuation of the spinal cord, contains the cardiac centre, respiratory centre and vasomotor centre, which respectively control the rate and force of heartbeat, the rate and depth of breathing and the diameter of blood vessels
ascending tracts (spinal cord)
sensory axons carrying impulses upwards towards the brain
descending tracts (spinal cord)
motor axons carrying impulses downwards away from the brain
division of peripheral nervous system
afferent and efferent
afferent division
involves sensory neurons carrying impulses into the CNS
somatic sensory neurons carry impulses from the skin and muscles.
visceral sensory neurons carry impulses from the internal organs
efferent division
involves motor neurons carrying impulses away from the CNS
autonomic division involves carriage of impulses to heart muscle, involuntary muscles and glands. (2 neurons)
somatic division involves carriage of impulses to skeletal muscles (1 neuron)
autonomic division (efferent)
sympathetic - fight or flight, activated when in times of strenuous activity, prepares body for such times. neurotransmitter involved = acetylcholine
parasympathetic - rest and digest, activated when in times of quiet activity; more regular bodily activities, controlling its constant, internal environment. neurotransmitter involved = noradrenaline
