Physiology

Harness as difference in electrical charge between the inside and outside of their cells. They are electrically active.

They are more negatively charged on the inside than the outside. This electrical potential difference is located immediately adjacent to the cell membrane.

A selectively permeable membrane and a differential distribution of charged ions across the membrane

• Inside: 15mM
• Outside: 150 mM

• Inside: 150 mM
• Outside: 5 mM

Pumps 3 Na+ out of the cell for every 2 K+ in. Uses ATP and is not critical between every action potential, but needed in the long run to establish concentration gradient.

+60 mV

-90 mV

• - It is -70 MV
• - Large diffusion of K+ out
• - Small diffusion of Na+ in
• - No diffusion of anionic proteins

The ease with which an ion can travel across a membrane. The greater an ion's permeability, the greater the ion's influence on the membrane voltage.

50:1. So K+ is 50 times more permeable than Na+, because there are a greater number of open K+ channels at rest.

More positive inside the cell

More negative inside the cell

• - Increase the permeability of the membrane to Na+
• - Decrease the relative permeability of K+

• -Increase the permeability of the membrane to K+
• - Decrease the relative permeability of Na+

A graded potential whose amplitude and duration can vary depending on the strength and rate of the application or removal of the stimulus. The stronger the stimulus the greater the permeability change and the larger the generator potential. They have no refractory period so summation is possible. They must be converted into APs to travel long distances.

Open

• -The activation gate is closed and inactivation gate is open
• - the channel is non-conducting but is ready to be activated by a depolarization

• Positive Feedback. The initial depolarization opens some avaiable Na+ channels. The Na+ influx results in further membrane depolarization, the more depolarized the
• better chance that the activation gate of available Na+ channels will be opened.

The activation gate of both channels is closed. The Na+ channel inactivation gate is likely open. (K+ has no inactivation gate)

Both the inactivation and activation gate of Na+ channel are open. The activation gate of K+ is closed.

The inactivation gate of Na+ channels has closed and the activation gate of K+ channels is open.

The activation gate of Na+ channels is closed, and the inactivation gate remains closed. The activation gate of K+ remains open.

The Na+ channel inactivation gate opens and the channels is now int he available state. The closing of K+ activation gates results in the membrane returning to resting membrane potential

The portion of the membrane that has just undergone an AP cannot be restimulated. This period corresponds to the time during which the Na+ gates are not in their resting conformation.

The membrane can be restimulated but requires a stronger stimulus than is usually necessary. This period corresponds to the time during which the K+ gates that were opened during the AP have not yet closed. (Na+ gates must be in resting conformation)

• - Voltage gate Na+ channels will remain inactivated
• - Increased conductance of K+
• - AP generation would be impossible
• - lethal injection: high does of KCl elevates extracellular K+ levels = prolonged depolarization.

The passive movement of charge. Current enters the axon through ion channels, depolarizing that region of the membrane. the positive charge is attracted to adjacent negatively charged regions of the membrane, this spreads the depolarization.

As current travels along the axon, charge leaks outwards across the membrane, aka electrotonic decay. Depolarization decreases as you move along the membrane.

The ratio of the Axial Resistance and the Membrane resistance. Increasing the diameter of the axon decreases axial resistance. Decreased axial resistance and/or a increase in membrane resistance increases the propagation.

Action potentials activate voltage-gated channels along axonal membranes to regenerate depolarization. "Boosting" with voltage-gated channels regenerates inward current and counteracts outward current leak in an unmyelinated axon.

• - The diameter of the fibre
• - The amount of membrane capacitance

Increasing the diameter results in decreased axial resistance. This increases the flow of current which results in more charge per until time reaching neighbouring membrane segments. Neighbouring membrane segments reach AP threshold more rapidly.

• A capacitor is two conductive plates separated by an insulator. So capacitance refers to the distance between extracellular and intracellular fluid across the membrane. it is inversely proportional to the distance between the two membranes.
• -Less capacitance = less time required to charge the membrane to threshold, greater rate of AP firing
• Membrane capacitance can be reduced by increasing the thickness of the membrane with myelin.

Formed from schwann cells in the PNS and oligodendrocytes in the CNS. The myelin coating acts as an insulator to prevent current leakage. Myelinated fibres APs travel up to 50 times faster. Myelin has no channels so less energy is requires, less ATPase activity.

• -The AP travels elecrotoncally - passively
• - The capacitance of the membrane is low
• - The charge time of the membrane is short
• - The membrane is resistance is increased
• - Depolarization propagates rapidly

• - Active propagation of the action potential
• - Membrane capacitance is greater
• - the charge time of the membrane is longer
• - There is a concentration of Na+ channels
• - The action potential slows down

On the cell body and dendrite of the postsynaptic neuron

• 1. AP propagation in presynaptic neuron
• 2. Calcium enters into the synaptic knob due to depolarization at end of axon
• 3. Neurotransmitter is released into synaptic cleft by exocytosis
• 4. Neurotransmitter binds to postsynaptic receptors
• 5. specific ion channels open in the subsynaptic membrane.

Induces a conformational change in the receptor, opening a channel pore. The resultant ion movement through the pore generates synaptic current. This generates a postsynaptic potential

Is either excitatory or inhibitory. Determines whether or not the postynaptic neuron will fire. You can have temporal and spatial summation of PSP's. Involve the passive movement of charge so have no refractory period. They are graded.

You can add PSP's up until you have a strong enough depolarization to cause an AP.

Taking information from the different branches (different synaptic clefts on dendrites that all go into the same cell body) and adding all the information up.

Usually requires the activation of more than one excitatory synapse to initiate an AP. EPSP is formed by the binding of excitatory neurotransmitters to bring Vm closer to AP threshold.

Bind to receptors that generate depolarizing PSP's to create an EPSP by bringing Vm to AP threshold. The most common one is glutamate. AMPA type glutamate receptor allws both Na+ and K+ ions through the open pore, this generates at EPSP with an equilibrium potential of 0.

When inhibitory neurones bind to receptors that generate PSP's that keep Vm from reaching AP threshold. An IPSP will either move Vm away from AP threshold or hold it at ECl preventing any subsequent depolarization. It is centered around the soma.

Bind to receptors that generate PSP's and keep Vm from reaching AP threshold. A common one is GABA. GABA receptor gated channels allow the entry of Cl- ions generating and IPSP with a potential equal to ECl.

A specialized synapse between an alpha motor neuron and skeletal muscle. It innervates at least one muscle fibre - motor unit. It is always excitatory, and an end plate potential is always large enough to cause muscle contraction.

• 1. AP in alpha motor neuron propagates to nerve terminal
• 2. It opens voltage gated calcium channels in the axon terminal
• 3. calcuim entry triggers the release of acetylcholine via exocytosis
• 4. Ach activates nicotinic receptors in muscle membrane. The activation of these receptors causes a larger suprathreshold end plate potential in the muscle fibre.
• 5. The EPP triggers and AP in the muscle cell memebrane (sarcolemma).

a bundle of axons situated outside the CNS

a bundle of axons travelling within the CNs

telencephalon and diencephalon

the mesencephalon

the metencephalon (pons) and the medulla. The cerebellum is an outgrowth of the hindbrain.

the cerebrum and the basal ganglia

The site of the highest level of neuronal processing. Responsible for motor activity, sensory perception, conciousness, etc... cerebral cortex is outer layer of grey matter.

involved in motor control

Thalmus and Hypothalmus

Important relay station for processing information going to the cerebrum.

Fundamental role in regulation autonomic bodily functions

Midbrain, pons and medulla. All levels of the brainstem contain tracts of white matter (Carrying info from cortex). The brainstem also contains the nuclei responsible for the function of the cranial nerves.

• - Nucleus in CNS
• - Ganglia in PNS

spinal cord---> brain

brain ---> spinal cord

• Receives and integrates all incoming sensory synaptic input. It forms the central core of the brainstem and has 3 functions:
• -Ascending: responsible for the generation and maintenance of arousal and consciousness.
• -Descending: Responsible for the generation and maintenance of muscle tone.
• - Respiratory and cardiovascular centers are located in the medulla.

• -8 cervical
• -12 thoracic
• -5 lumbar
• -1 coccygeal

Are filled with CSF. CSF leaves the ventricular system via apertures between the cerebellum and the medulla.

Produces CSF constinuously

• -Pia Matter
• -Arachnoid membrane
• -Dura matter

Highly vascularized, adheres to the surface of the brain and spinal cord. It faithfully follows the indentations of the surface. Innermost layer.

Fits loosely over the surface. Creates a space between itself and the pia matter called the subarachnoid space, beneath which is situated the CSF. It has a rich blood supply, and the CSF is resorbed back into the blood at this point.

Very thick and though, has a protective function. Outermost layer.

• - Buoyancy effect : protects against the tendency of various forces to distort the brain.
• - Excretion of wastes
• - Transport of hormones

Carry information towards the CNS

Carry information away from the CNS

• Nerves are composed of bundles of axons
• -sensory (afferent)
• -motor (efferent)

• -innervated striated muscle fibres
• -have their cell body in the CNS (except autonomic)
• - release acetylcholine - which acts via nicotinic receptors at neuromuscular junctions

-have their cell body outside the CNS in sensory ganglia

• In the PNS are either sympathetic or parasympathetic.
• -There are 2 neurones in the pathway from the CNS to the peripheral organ.
• 1. Preganglionic
• 2. Postganglionic

- has its cell body in the CNS

• It is an autonomic ganglion in the periphery.
• -in the sympathetic system the ganglion is close to the CNS and releases norepinephrine.
• -in the parasympathetic system the ganglion is close to or actually within the target organ and releases acetylcholine.

• Preganglionic is long
• Post ganglionic is short

• Preganglionic is short
• Post ganglionic is long

• Homeostasis
• Controls vegetative systems (coordinates with endocrine system)
• Blood Pressure (HR, SV, resistance)
• GI motility
• Salt/Water balance
• Pupillary reflexes
• Sexual function

• Reflexes at the spinal cord level
• medulla - within the brainstem
• hypothalmus
• prefrontal cortex

• increased heart rate, SV, and BP
• increased blood flow to skeletal muscle
• decreased blood flow to skin
• fight or flight response -release of epinephrine from adrenal medulla stimulates skeletal muscle glycogenolysis

• decreased HR, SV, and BP
• increased GI motility
• Relaxation of sphincters in esophagus, stomach and bladder
• done by acetylcholine

Both sympathetic and parasympathetic systems are activated during intense conflict situations

originate inside the cranium and can carry afferent, efferent and ANS fibers

OLFACTORY - sense of small (sensory)

OPTIC - Vision (Sensory)

OCCULOMOTOR - moves eyeball medially (motor, voluntary) and constricts pupil (motor autonomic-parasympathetic)

TROCHLEAR - Moves eyeball (motor voluntary)

TRIGEMINAL - Mastiation (motor, voluntary) and touch, temperature and pain from face and head (sensory).

ABDUCENS - moves eyeball laterally (motor voluntary). III and VI work together by information carried in the medial longitudinal fasiculus.

FACIAL - Muscles of facial expression (motor, voluntary), lacremal and salivary glands (motor, autonomic -para) and tastebuds of anterior 2/3 of tongue (sensory).

AUDITORY - Hearing from cochlea and gravity, motion and position of the head from vestibular apparatus (sensory).

GLOSSOPHARYNGEAL - Pharynx swallowing (motor, voluntary), salivary glands (motor, autonomic-para), tastebuds in anterior 1/3 of tongue, monitors CO2 and O2 in blood by carotid chemoreceptors, and monitors BP by carotid sinus baroreceptors (sensory)

VAGUS - Pharynx swallowing, larynx phonation (motor, voluntary), slows heart rate and controls abdominal secretions (motor autonomic-para), sensory info from baroreceptors and chemoreceptors and from GI tract.

ACCESSORY - Swallowing and shoulder shrugging (motor, voluntary)

HYPOGLOSSAL - Tongue (motor, voluntary)

• 8 cervical
• 12 thoracic
• 5 lumbar
• 5 sacral
• 1 coccygeal

The upper thoracic spinal nerves

All thoracic and the first and second lumbar segments

Cranial nerves III, VII, IX, and X, and sacral 2,3 and 4.

sacral segments 2, 3,and 4.

• olfaction - I
• vision - II
• taste - VII and IX
• hearing and balance - VIII

IV (trigeminal) and all spinal nerves except C.1

Are transducers that convert one form of energy into another form. They detect stimuli and turn them into action potentials.

• photoreceptors - rods and cones of retina
• thermoreceptors - changes in temperature, central (hypothalmus) and peripheral (skin)
• nociceptors - pain
• mechanoceptors - mechanical stimuli

a depolarization of the peripheral, receptive portion of the sensory axon. It is cause by a sensory stimulus (except in rods and cones, the GP is a hyperpolarization).

• It can be graded in amplitude (the bigger the stimulus, the bigger the GP)
• doesn't cause the membrane to be refractory
• is not actively propagated

• are all or none
• cause the membrane to be refractory
• are actively propagated by regenerating themselves along the axonal membrane

the opening or closing of ion channels resulting in a depolarization

• is a direct effect of mechanical stimuli on stretch sensitive channels
• is non selective and allows both Na and K to pass
• the net result is a depolarization

is a G-coupled mechanism that influences the channel indirectly

• frequency coding
• population coding

the greater the intensity, the greater the frequency of action potentials in individual axons

with increased intensity, more individual receptors are recruited

Important in areas where it is valuable to maintain information about a stimulus. They monitor static, unchanging stimuli such as maintained muscle length and maintained pressure (ruffini endings)

detect the onset of the stimulus or respond with a slight depolarization when the stimulus is removed. Detect change in time (vibration - pacinian corpuscle) or change in space (meissner's corpuscle)

• a rapidly adapting skin receptor
• contains concentric layers of CT wrapped around the peripheral terminal of an afferent neuron
• as the stimulus continues, the pressure energy is dissipated because the layers slip, the receptor no longer responds and you get adaptation.

• rapidly adapting
• involved in discriminative touch
• meissner's are abundant in fingertips

• slowly adapting
• signal non-changing features of tactile stimuli - maintained pressure

• by receptors which are free nerve endings
• there is no associated capsule or specialization

• 1. based on conduction velocity, uses A,B,C, designation
• -A: fastest conduction velocity, large diameter, myelinated
• -B: smaller diameter, ssi
• 2. based on the diameter and uses I,II,II,IV