An ACTION POTENTIAL is a rapid rise and fall in voltage or membrane potential
across a cellular membrane.
1. Resting Membrane Potential
2. Threshold for Excitation
An ACTION POTENTIAL occurs when a neuron sends information down an axon,
away from the cell body.
• This is the resting membrane
Potential before the Action Potential
• The membrane is said to be
“POLARIZED” during this stage
• Because of the -90 millivolts negative
membrane potential that is present.
• In this stage, the open channels in
the plasma membrane are
predominantly the “POTASSIUM
Here, the membrane suddenly becomes
very permeable to Sodium (Na+) ions;
Allowing tremendous numbers of
positively charged sodium ions to diffuse
into the interior of the axon.
The normal “POLARIZED” state of -90mV
is immediately neutralized by the
inflowing positively charged sodium ions
This is called DEPOLARIZATION.
• ABSOLUTE REFRACTORY PERIOD: The period from the initiation of the
action potential to immediately after the peak. This is the time during
which another stimulus given to the neuron (no matter how strong) will
not lead to a second action potential.
• RELATIVE REFRACTORY PERIOD: the period that occurs during the
undershoot phase; where an action potential can be activated but only
if the trigger (stimulus) is large enough.
• LATERAL INHIBITION is the
capacity of an excited
neuron to reduce the activity
of its neighbors.
• Lateral inhibition disables
the spreading of action
potentials from excited
neurons to neighboring
the lateral direction.
OF THE RED
• Regulates muscle tone (motor coordination)
• Increases muscle tone of flexors
• Reduces muscle tone of extensors
• Straightening and Statokinetic
a reflex that corrects the orientation of the body
when it is taken out of its normal upright position.
receptors of the vestibular analyzer (unnatural
turn the head upside crown
proprioceptors of neck muscles
redistribution of muscle tone of trunk and extremities
animal becomes a natural position
• Postural reflex that is initiated by stimulation of the semicircular
canals through movements of the head and involves compensatory
movements of the limbs and eyes.
• Reflexes to preserve posture and maintain a balance in the event of
acceleration (horizontal, vertical, angular).
• Condition characterized by a sharp increase in muscle tone of extensor muscles
• Decerebrate posturing indicates brainstem damage (midbrain), specifically damage below the
level of the red nucleus.
• Located in the basal ganglia
• Made up of 2 parts: Pars Compacta & Pars
• Substantia Nigra Pars Compacta (SNc) however,
produces the neurotransmitter DOPAMINE
• Substantia Nigra Pars Reticulata (SNr) however,
produces the neurotransmitter GABA (Gamma
• Caused by loss of dopamine secreting cells
in the Substantia nigra.
• Parkinson's disease is a progressive
nervous system disorder that affects
• Symptoms start gradually, sometimes
starting with a barely noticeable TREMOR
in just one hand.
• Tremors are common, but the disorder also
commonly causes STIFFNESS or RIGIDITY.
• Medulla oblongata or medulla is
the lowermost part of brain. It is
situated below pons and is
continued downwards as spinal
• It also has many important
centers which control the vital
• Cranial nerves are
the nerves that emerge directly
from the brain in contrast
to spinal nerves (which emerge
from segments of the spinal
• Ten of the cranial nerves
originate in the brainstem
• For HEARING and BALANCING
• Ear consists of three parts, namely
External Ear, Middle Ear and Internal Ear.
• External ear is formed by two parts:
• 1. Auricle or pinna
• 2. External auditory meatus.
• The middle portion of the ear that is located internal to the tympanic membrane and
external to the oval window of the inner ear,
• Middle ear or tympanic cavity is a small, narrow, irregular, laterally compressed chamber,
situated within the temporal bone.
• Middle ear consists of the following structures:
• 1. Auditory ossicles (Malleus, Incus, Stapes)
• 2. Auditory muscles (Tensor Tympani & Stapedius Muscle)
• 3. Eustachian tube (auditory tube or pharyngotympanic tube).
• A canal in the posterior
wall of the tympanic
• Allows communication
with the Mastoid Air cells
located in the MASTOID
• Made up of the bony labyrinth and
• The innermost portion of the ear that
contains organs of hearing
(i.e., cochlea) and equilibrium (i.e.,
vestibule) and is situated within the
petrous part of the temporal bone.
• Important for controlling the whole-body movement and equilibrium are the brain
stem’s RETICULAR NUCLEI & VESTIBULAR NUCLEI
• RETICULAR NUCLEI
• PONTINE & MEDULLARY RETICULAR NUCLEI
• THE PONTINE RETICULAR NUCLEI --- transmits excitatory signals
• THE MEDULLARY RETICULAR NUCLEI --- transmits inhibitory signals
• … to anti-gravity muscles
• The vestibular system can be divided into the vestibular apparatus & central
• Vestibular Nuclei: Superior, Lateral (Dieters’), medial, inferior
• Function in association with the pontine reticular nuclei to excite the anti-gravity
• Without this support of the vestibular nuclei, the pontine reticular system would
loose much of its excitation of the antigravity muscles.
• Semi-Circular Ducts:
• Anterior, Posterior, Lateral
• Arranged at right angles to one
another so that they represent all
three (3) planes in space
• For ANGULAR ACCELERATION
• Utricle & Saccule
• For LINEAR ACCELERATION
• Utricle = Horizontal Acceleration
• Saccule = Vertical Acceleration
Accommodation is the process of
adjusting the lens of the eye so that you
can see both near and far objects clearly.
Very rapid process
Accommodation is controlled by
muscles connected to the lens, called
This Ciliary muscle can contract and
increase the curvature of the lens so
that the lens thickens.
• FOCUS ON NEAR OBJECTS
• Ciliary Muscles Contract around the lens
• Increasing the curvature of the lens;
• So that it thickens
• Making the lens more spherical
• FOCUS ON DISTANT OBJECTS
• Ciliary Muscles Relax around the lens
• Decreasing the curvature of the lens
• Making the lens less spherical
REFLEX: A reflex, or reflex action, is an
involuntary and nearly instantaneous
movement in response to a stimulus.
Reflexes help protect your body.
A reflex is made possible by neural
pathways called reflex arcs.
• Neural activity is initiated at the border between
the nervous system and the outside world by
• Receptors are either specialized endings of
afferent neurons themselves or separate cells that
affect the ends afferent neurons.
• LOCATION: Different areas of the body like the
Skin, Muscles & Tendons
• Proprioceptors are the receptors, which
detect and give response to movement
and change in position of different parts of
• These receptors are also called Kinesthetic
• LOCATION: Proprioceptors are situated in
labyrinth, muscles, tendon of the muscles,
joints, ligaments and fascia
• Muscle spindles are stretch
receptors within the body of
a muscle that primarily detect
changes in the length of
• They convey length information
to the central nervous system via
afferent nerve fibers.
• ****MUSCLE LENGTH***
• MUSCLE STRAIN --- A muscle
strain is the stretching or tearing
of muscle fibers.
• LOCATION: Tendon of skeletal muscle
• Golgi tendon organ gives response to
the change in the force or tension
developed in the skeletal muscle during
• The system helps to control BP, GIT motility, GIT secretion, Urinary
bladder emptying, Sweating, Body temp, etc.
• Divided into:
• Sympathetic NS
• Parasympathetic NS
• Often referred to as Rest - and - Digest
• Parasympathetic Neurotransmitter ACETYLCHOLINE
• Nerve Fibers are called Cholinergic Fibers
• Receptors: M receptors and N receptors
• M Skin, Eye, Smooth Muscles, Lungs (Bronchus)
• N Ganglia, Synapses of Skeletal Muscles, Adrenal Medulla (Enterochromaffin Cells)
• Associated with CN X (Vagus Nerve)
• Often referred to as Flight - Or - Fight
• Sympathetic Main Neurotransmitter NOREPINEPHRINE
• Nerve Fibers are called Adrenergic Fibers
• Receptors: 𝜶 receptors and 𝜷 receptors
• 𝜶 RECEPTORS Skin, Mucous Membranes, Vessels, Glands, Organs of the Abdominal Cavity
• 𝜷 RECEPTORS Heart, Lungs (Bronchus), Skeletal Muscles, Organs of the Abdominal Cavity,
Vessels, Eye (Ciliary Muscle)