exam 3 bbb

Function of the vestibular system

balance, maintenance of the head in an upright position, adjustment of the eye movement relative to head movement

components of the vestibular system

vestibular sacs and semicircular canals

Vestibular Sacs

Respond to the force of gravity, inform brain about the head’s orientation

Semicircular Canals

Respond to angular acceleration and sudden rotation of the head

Three major planes of the head

Sagital, transverse, horizontal

anatomy of the vestibular system

three fluid filled tubes arranged at right angles to each other

Ampulla

An enlargement that contains a gelatinous mass called the cupula in which the sensory hair cells are embedded.

Anatomy of the vestibular sacs (the utricle and the saccule)

Roughly circular and contain a patch of receptive tissues; on the floor of utricle and wall of saccule. The receptive tissue contains hair cells.

Somatosenses

Senses relates to touch, pain, temperature, and body position & processed by the somatosensory system.

Cutaneous sense

skin sense, sensitive to touch; pressure, vibrating, temperature, and pain

Proprioceptiom

Perception of body’s position and posture; location of the body in space

Kinesthesia

Perception of the Boyd’s own movement; receptors within the joint respond to the magnitude and direction of limp movement and also changes in the stretching of skin

Organic senses

Receptors in and around the internal organs; ex- stomachache, gallbladder attack

mechanoreceptors

A sensory neuron that responds to mechanical stimuli (pressure, stretch, vibration, etc)

Types of skin

hairy skin and glabrous skin

Hairy skin

Most of the body surface

Glabrous skin

Palms and soles of feet

Types of cutaneous receptors

encapsulated receptors and free nerve endings

Encapsulated receptors

Markel’s disks, Ruffini corpuscles, meissners corpuscles, pacinian corpuscles

Merkel’s Disks

Detection of form, roughness (especially finger tips)

Ruffini Corpuscles

Deception of pressure

Meissner’s corpuscles

Detection of edge contours

Pacinian corpuscles

Detection of vibrations

Free nerve endings

Pain and temperature, pleasurable touch

touch (tactile stimulation)

• detected by mechanoreceptors, analyze shape and texture

• Movement of dendrites opens mechanical ion channels and generates receptor potential

• Precisely localized

• Precise use of fingertips associated with changes in somatosensory complex

Temperature

• It’s a relative sense, not absolute (skin adapts to set point)

• Two categories of temperature receptors; cool (close to surface) & warm (deeper in skin)

Pain

• uses a network of free nerve endings

• Two types of receptors:

• 1. High threshold mechanoreceptors - intense pressure

• 2. Capsaicin - extreme heat, acid, capsaicin

• Synapses in the spinal cord and ascends to the cortex contralaterally

Gustation

Scientific term for the sense of taste, specifically the act or sensation of tasting

Papillae

Small bumps on the tonnage that contains most of the taste buds

Taste Buds

• Are taste receptor calls

• Arranged in groups of 20-50

• Have cilia that project out of the pore into the saliva

• Form synapses with dendrites of bipolar neurons

• The axons of the bipolar neurons project taste info. Into the brain through 7th, 9th, and 10th cranial nerves.

• Their neurotransmitters is ATP

Salty

Sodium ions enter through ion (Na+) channels and depolarize the cell

Sour

Acidic - hydrogen ions enter through ion channels and depolarize cell

Sweet

Sugars bind receptors coupled to a G protein called buster in. Receptor family TIR2 and TIR3

Bitter

Organic molecules (alkaloids), also through hustducin. Receptor family T2R

Umami

Glutamate binds receptors coupled to G proteins gustducin and transduction. Receptor family T1R1 and T1R3

Olfaction

the scientific term for smelling or the sense of smell

Olfactory epithelium

• Patches of mucous membrane that contains most the cilia of the olfactory receptors; each receptor sends a single axon into the olfactory bulbs located at the base of the brain

• Those axons form synapses with dendrites of mitral cells in a bundle named olfactory glomerulus

• Each glomerulus receives information from only one type of receptor cell, and makes synaptic contacts with a single mitral cells

Olfactory tract axons project to:

1. The amygdala

2. Entorhinal cortex

3. Piriform cortex

Skeletal Muscles

• responsible for voluntary body movements

• Connected to bones at each end through tendons

• In pairs of “flexor” and “extensor”

Types of muscle fiber

Extrafusal and intrafusal

Extrafusal

• responsible for the force exerted by muscle contraction

• Served by axons of alpha motor neurons

Intrafusal (muscle spindles)

• detects stretch (changes in muscle length)

• Served by axons of gamma motor neurons

Motor unit

An alpha motor neuron, its axon, and associated extrafusal muscle fibers

Striations

• dark stripes caused by the overlap of actin and myosin filaments in a muscle fiber

Muscular contraction

A motor neuron axon and a muscle fiber make a synapse called neuromuscular junction. Firing of the neuron releases acetylcholine which causes a depolarization of the postsynaptic membrane (called end plate potential) that will open calcium channels and always results in firing the muscle fiber that will cause contraction.

Sensory feedback from muscles

Intrafusal muscle fibers have sensory endings sensitive to stretch (muscle spindles). When the muscle lengthens, a gamma motor neuron fires, the intrafusal fibers contract, muscle spindle is activated and the alpha motor neuron causes the Extrafusal fibers contract to contract.

Polysynaptic tendon reflex (important for posture)

• when a muscle suddenly stretches, two groups of affront axons get activated:

• 1. More sensitive to stretch → tell the brain how hard the muscle is pulling.

• 2. Less sensitive to stretch → synapse on inhibitory interneurons in the spinal cord → inhibitory interneurons synapse on the alpha motor neuron and release glycine → alpha motor neuron is inhibited → muscle won’t contract.

Motor homunculus

• The spatial representation of the specific cortical areas that control specific body movements

• A disproportionally larger amount of the cortical area is devoted to movement of fingers and muscles involved in speech.

Descending tracts of neurons in the primary motor cortex

1. Lateral group: control of independent limo movement; ex hands and fingers

2. Ventromedial group: control of automatic movements; ex. Trunk and limb movements involved in posture and locomotion

Motor association cortex

1. Supplementary motor cortex; involved in learning and performing behaviors that consist of sequences of movement

2. Pre motor cortex: involved in learning and executing complex movements that are guided by arbitrary sensory information

Basil ganglia

Receives info, from the cerebral cortex, project into primary motor cortex and motor association cortex.

Motor nuclei

Caudate (striatum)

Putamen (striatum)

Globus pallidus

Parkinson’s disease

Results from loss of dopaminergic neurons of the nigrostriatal bundle (substantia nigra)

Huntington disease

Degeneration of the caudate nucleus and putamen especially of GABAergic neurons

Cerebellum

Plays an important role in coordination of movement. Output projects to every major structure in the brain.

Irregular postural reflex

Damage to flocculonodular love

Impaired balance

Damage to vermis

Leg rigidity

Damage to intermediate zone

Weakness and decomposition of movement

Damage to lateral zone