Download Class 3 - Nervous System Part 2

Synapse
• Junction between two neurons
• Synaptic Knobs: Axon Terminal
• Neurotransmitters
– When the action potential reaches the axon
terminal, the neurotransmitters are released
from the vessicles.
– Some are Excitatory: continue the impulse
– Some are Inhibitory: stop the impulse
Reflex Arc
Reflexes
• Knee-Jerk Reflex (Patellar Reflex)
– Stimulates stretch receptors in the Quads
– Send an impulse to the femoral nerve to
contract the Quads
• Withdrawal Reflex
– Temperature or Pain Receptors are triggered
– Sends an impulse to CNS (spinal cord)
– Causes flexors to contract
Types of Senses
Types of Sensory Receptors
• Chemoreceptors: chemicals become
attached to receptors on their
membranes. Smell and taste
• Pain Receptors (Nociceptors):
extreme chemical or thermal stimuli.
Free nerve endings
Types of Sensory Receptors
• Thermoreceptors: respond to changes in
temperature. Heat and cold receptors
• Mechanoreceptors: compression,
bending, stretching of cells. Touch,
pressure, proprioception, hearing, and
balance
• Photoreceptors: respond to light: vision
Referred Pain
• Crossed wires in the cerebral cortex
because the pathways are close together.
• Sends signals to the skin instead of back
to the organ where it originated.
• Most sensations happen in the skin so the
brain plays the odds and sends it to the
skin.
Touch, Pressure, and Vibration
• Free Nerve Endings:
– Simplest, most common sensory receptor
– Scattered through most of body
– Extreme touch, pressure or vibration
• Meissner’s Corpuscles
– Used to determined texture of objects. Fine
descrimination.
• Pacinian Corpuscles
– Deep cutaneous pressure; vibration
Temperature Sensation
• Free Nerve Endings
– Throughout body
– Detect extreme temperatures as pain
• Heat and Cold Receptors
– 10 to 15 times more cold receptors
Pain Sensation
• Free Nerve Endings:
– Stimulated by tissue damage (swelling)
• Pain nerve fibers:
– Acute: sharp pain, myelinated fibers, pain
stops when stimulus is removed (superficial)
– Chronic: aching pain, unmyelinated fibers,
pain continues when stimulus is removed
(deep)
Pain Sensation
• Visceral Pain and Referred Pain
– Visceral pain: fewer receptors so it is more of
a dull ache
– Referred Pain: impulse travels to cutaneous
tissue instead of visceral tissue
• Regulation of Pain Impulses
– Prevent nerve cells from releasing more pain
signals
– Endorphins and enkephalins - opiates
Muscle Spindles
Stretch Reflex
• When muscle is stretched, the motor
neurons are stimulated and cause
stretched muscles to contract and shorten
back to its resting length.
• Stretch too far – pulls muscle back
• Protective – to keep muscle from tearing
Golgi Tendon Organs
Golgi Tendon Organs
• Too much strain (weight) on the muscle
causes muscle to contract too hard
• Muscle relaxes so you drop the weight
• Protective reflex to keep muscle from
tearing
Olfactory Receptor
Sense of Smell (Olfaction)
• Neurons from the CNS directly contact
the outside environment
• Chemoreceptor – distinguish between
chemical changes
• Structure: Unipolar neurons
• Function: Detect chemical changes in the
air
Sense of Taste (Gustation)
• Taste bud structure:
– On tongue and pharynx
– 40-60 layers of epithelium
shaped like an onion
• Function:
– Detects chemical changes in
aqueous solution
Taste Nerve Pathway
• Cranial Nerves
– VII (Facial) – Anterior 2/3 of tongue
– IX (Glossopharyngeal) – Posterior 1/3 of
tongue and part of roof of mouth
– X (Vagus baby) - throat
• Quick Adaptation
– Palate needs to be reset
Sense of Hearing
External Ear
• Ear (auricle)
• External Auditory Meatus – ear canal
• Tympanic Membrane (ear drum)
– Vibrates in response to sound and is semitransparent
• Function:
– Collect sound waves to be sent to the middle
ear
Middle Ear
• Structure:
–Auditory Ossicles
• Malleus – connects to eardrum
• Incus – connects malleus to stapes
• Stapes – connects to inner ear
More Middle Ear
• 2 small muscles
Shock absorbers – pulls bones back so they
won’t vibrate so hard if there is a loud noise
• Tensor tympani – connects to malleus and wall of
middle ear
• Stapedius m. – connects stapes to wall of middle ear
– Tympanic Reflex – protect receptors from loud
sounds
• When muscles contract they pull the malleus and
stapes away from the ear drum and inner ear
• 40 millisecond lag time
Even More Middle Ear
• Eustachian tube
– Connects middle ear to pharynx (back of
throat)
– Allows drainage of fluid and pressure changes
(equalization)
– Bacteria can gain access to middle ear
• Function of Middle Ear:
– Transmit vibrations from ear drum to inner ear
Inner Ear
• Cochlea
– Shell shaped
– Houses hearing receptors
• Osseous Labyrinth
– Hollow area inside of shell
• Membranous Labyrinth
– Like a pool liner inside osseous labyrinth
• Round and Oval Windows
– Holes in the bone that the vibrations pass through
– Stapes connects to the oval window
More Inner Ear
• Organ of Corti
– Hearing receptor
– Stimulated by vibrations in the
watery/gelatinous fluid (tectorial membrane) in
the cochlea
• Function of the Inner Ear
– Carries impulses to brain via the
vestibulocochlear nerve VIII
Sense of Equilibrium
• Static Equilibrium
– Movement in a straight line
– Impulses picked up by the Vestibule and
carried to brain via Cranial Nerve VIII
– Macula are the receptors
– Function: balance
More Equilibrium
• Dynamic Equilibrium
– Movement in many directions or a spin
– Impulses picked up by the semicircular canals
– Crista Ampularis is the receptors
– Function: to detect rotational changes in the
body
Sense of Sight
• Function of the Eye:
– Allow light through so the impulse can be sent
to the brain
Sense of Sight
• Accessory Organs
– Eyelids: keep junk out
– Medial and Lateral Canthus
– Eyelashes
Lacrimal Apparatus: glands and
ducts
• Produce tears
• Lubricates the eye
Extrinsic Eye Muscles
6 skeletal muscles that move the eye
• Controlled by Cranial Nerves III, IV and VI
External Anterior Structures
• Cornea
• Conjunctiva
Structure of the Eye
• Three Tunics
– Sclera - White
– Choroid - dark
– Retina - photoreceptors
Retina
• Fovea Centralis – area of best vision
• Optic Disc
• Optic Nerve
Anterior Structures
• Lens and Ciliary Muscles
– Contract and pull lens to flatten it out
• Iris - Colored part
– Controls the size of the pupil
Chambers of the Eye
• Anterior Cavity – Aqueous Fluid
• Posterior Cavity – Vitreous Fluid
Pathway of Light Through the Eye
• Refraction
• Accommodation
Visual Fields and Pathways to the
Brain
• Optic Chiasma
• Optic Tracts
• Optic
Radiation
Eye Reflexes
• Convergence
• Photopupillary Reflex
Accommodation Pupillary Reflex