Neuro Final

Events of perception of a sensation

1. Stimulation of the Receptive Field of a sensory neuron a. Receptive Field: an area with in which a stimulus of appropriate quality and strength will cause a sensory neuron to initiate a nerve impulse. 2. Transduction (Conversion) of the stimulus (a sensory receptor or sense organ must receive the stimulus and transduce the stimulus into an electrical response (generator potential); it will eventually lead to a nerve impulse. Each type of sensory receptor can only transducer one type of stimulus. 3. Generator Potential: an electrical response, when this generated potential reaches threshold (if it's large enough) will then generate and action potential in a sensory neuron. It elicits a nerve impulse that will be generated and conducted along a sensory pathway from the CNS to the PNS. It is not propagated like an action potential. 4. Impulse Generation and Conduction a. First Order Neuron: a sensory neuron that conducts impulses from somatic receptors (periphery) to the spinal cord and the brainstem. b. Second Order Neuron: synapses with a first order neuron in the brainstem which will conduct impulses from the spinal cord and the brainstem up to the thalamus. c. Third Order Neuron: synapses with a second order neuron in the thalamus. They relay impulses from the thalamus up to the somatosensory cortex (post-central gyrus) of the cerebrum where the conscious perception of the sensation is elicited. 5. Integration of the sensory input: a region of the CNS must receive and integrate the information that is carried by the action potential and converted to a sensation, this is the final pathway.

Action potential

A brief fluctuation in membrane potential caused by the rapid opening and closing of voltage-gated ion channels. Action potentials sweep like a wave along axons to transfer information from one place to another in the nervous system.

Eustachian tube/tympanic tube

A narrow tube between the middle ear and the throat that serves to equalize pressure on both sides of the eardrum

First order neurons location

A sensory neuron that conducts impulses from somatic receptors (periphery) to the spinal cord and the brainstem.

Receptor potential

A stimulus-induced change in the membrane potential of a sensory receptor.

C-fiber

An unmyelinated postganglionic fiber that provides slow nerve impulse transmission.

2 branches of cranial nerve 8

Cochlear and Vestibular

Photopigments

G-protein-coupled transmembrane proteins located in disks of membranes in the outer segments of rods and cones, change color & shape in response to changes in light intensity

Auditory receptors location

In the bony labyrinth and the inner membranous labyrinth.

What is the difference between damage to the upper and lower motor neurons? What would the patient experience?

Lower motor neurons extend from the brain stem and spinal cord to skeletal muscles. These lower motor neurons are called the final common pathway. Upper motor neurons (UMN) extend from the cerebral cortex (frontal lobe) to the anterior horn of the spinal cord as well as the pons and the medulla. The primary motor area of the cerebral cortex is the pre-central gyrus in the frontal lobe. The neurons in the frontal lobe are quite large; they allow conscious control over voluntary movements of skeletal muscle. These neurons have very long axons and they form massive voluntary motor tracts. Most of these neurons are involved with conscious motor control (skeletal muscle) of the face, the tongue, the hands, as well as posture, reflexes and muscle tone. Motor innovations are contralateral (opposite side). The left frontal lobe controls muscles on the right side of the body and vice versa.

Types of parasympathetic ganglia

Main type are terminal ganglia

What are the additional sensory pathways that we discussed?

Major indirect tracts such as rubrospinal (tracts that originate from the red nucleus and are responsible for motor input of gross postural tone), tectospinal (a contralateral tract that is responsible for postural muscle tone associated with auditory and visual stimuli and vestibulospinal (an ipsilateral tract that is responsible for gross postural adjustments in response to head movements).

Second order neurons location

Synapses with a first order neuron in the brainstem which will conduct impulses from the spinal cord and the brainstem up to the thalamus

Third order neurons location

Synapses with a second order neuron in the thalamus. They relay impulses from the thalamus up to the somatosensory cortex (post-central gyrus) of the cerebrum where the conscious perception of the sensation is elicited.

Events involved in hearing

The auricle directs sound waves into the external auditory canal Sound waves strike the tympanic membrane causing it to vibrate. The vibration conducts from the tympanic membrane through the ossicles, in the following order: malleus, incus, and the stapes. The stapes moves back and forth pushing the membrane of the oval window in and out. The movement of the oval window establishes pressure waves in the perilymph of the cochlea (scala vestibuli). Pressure waves in the scala vestibuli are transmitted to the scala tympani, which then pushes the vestibular membrane back and forth, which increases and decreases the pressure in the endolymph of the cochlea duct. These pressure changes in the endolymph move the basal membrane ever so slightly, which moves the hair cells of the spinal organ against the tectorial membrane. The bending of these hair cells produces receptor potentials that lead to action potentials, if the threshold is reached, along the cochlear nerve fibers of cranial nerve 8. Pressure changes in the scala tympani cause the round window to bulge outward into the middle ear.

Autonomic tone

The balance between the parasympathetic and sympathetic activity.

tympanic membrane

The eardrum. A structure that separates the outer ear from the middle ear and vibrates in response to sound waves.

Motor pathway

The motor pathway of the spinal cord is: Lower motor neurons - right anterior corticospinal tract - spinal cord and left lateral corticospinal tract - pyramid and decussation in the medulla - upper motor neurons - through the midbrain to the right side of the body.

Region of nervous system that controls defecation and urination

The parasympathetic rest and digest response.

Proprioceptors

They are located in skeletal muscles, tendons, joints, ligaments, in CT coverings of bones and muscles, in and around joints, and in the internal ear and are stimulated by stretching or movement. The provide information about body position, muscle tension, joint position and equilibrium. They transmit nerve impulses related to muscle tone, movement of body parts, body sensation and balance.

Dual innervation

They are organs that receive impulses from both sympathetic and parasympathetic fibers. Examples are the heart, blood vessels, kidney and lungs; one system overrides the other.

Parts of brain that make you aware of and able to remember taste

Through our sensory memory

Types of sympathetic ganglia

Two types of sympathetic ganglia are the Paravertebral Ganglia and the Prevertebral ganglia.

Define transduction

a conversion of the stimulus. The sensory receptor or sense organ must receive the stimulus and transducer the stimulus into an electrical response (generator potential), it will eventually lead to a nerve impulses. Each type of sensory receptor can only transducer one type of stimulus.

Vitreous humor

a more viscous, jelly-like fluid that keeps the eyeball spherical and is located between the lens and retina

Ruffini corpuscles

a single encapsulated myelinated nerve ending with multi- branched or sprayed axonal endings. Large receptor fields, slowly adapting. They represent 20% of the mechanoreceptors in the hand. They are found in the skin, ligaments and tendons. They are important in signaling heavy, continuous touch and pressure. They are important in regulating the degree of joint rotation.

Separate cells

a synapse with first order neurons located in sense organs; hair cells in the ears, rods and cones in the retina (eyes) and gustatory receptor cells on taste buds.

Aqueous humor

a watery fluid that nourishes the cornea and is located between the cornea and lens

Hair cell receptors

auditory receptors, they generate receptor potentials because they convert mechanical energy into electrical energy. There are outer and inner hair cell receptors that make up the cranial nerve and contract upon electrical stimulation.

Parasympathetic ganglia

autonomic ganglia, they are the rest and digest responses that conserve and restore body energy, digest and absorb nutrients, and eliminate waste products

External ear

collects sound waves and directs them towards the external auditory canal and consists of the oracle/pinna (elastic cartilage covered with skin).

Stapes location

connected to the oval window, and drives the fluid in the cochlea, producing a traveling wave along the basilar membrane

Middle ear

consists of an air-filled cavity in the temporal bone of the cranium, the round windows and the oval windows.

inner ear

contains a complicated series of canals and consists of the bony labyrinth (semicircular canals, the vestibule and the cochlea) and the inner membranous labyrinth.

One main function of hypothalamus

controls and integrates the autonomic nervous system

Photopigments found in cones

covalently linked proteins called opsin and chromophore

Cranial nerve involved in hearing

cranial nerve 8

Meissner's corpuscles

encapsulated nerve endings that elicit large myelinated sensory nerve fibers, they have small receptive fields and they rapidly adapt. They are found in the thermos of the skin, mostly non-hairy parts of the skin (lips, fingertips, palms of the hands, and soles of the feet. They provide for 40% of the sensory innovation to your hands. They are sensitive to weak stimuli. They are actually myelinated axon terminals that are formed by flattened Schwann cells.

Merkel's discs

flattened portions of dendrites of sensory neurons. They contact the stratum basale. Small receptor fields, slowly adapting. They provide for 25% of all mechanoreceptors. They are densely populated in the lips, fingertips, genitalia. They are found in association to hair follicles. Since they are slowly adapting they detect continuous touch of objects against the skin. They are important in determining the texture

sympathetic ganglia

flight or fight response in stress, fright or anger.

Free nerve endings

found everywhere in the skin and they detect pain (nociception), temperature, itch, tickle, touch, pressure and stretch

Coclear

has a spiral ganglion in the bony modiolus.

Neuroectodermal tunic (retina)

innermost layer, contains nervous tissue responsible for photoreception

Graded potential

is a wave of electrical excitation that corresponds to the size of the stimulus. in ligand/mechanically graded ion channels, they are localized and the amplitude depends on the stimulus strength. used by dendrites for returning signals from sensory organs. get weaker as they travel along nerve fibers and last for several milliseconds to several minutes.

Vestibular

it consists of the saccular, utricular and the ampullary nerves.

Pacinian corpuscles

lie in the dermis, hypodermis (subcutaneous level), and in deep fascial tissues; only stimulated by very rapid movements of the tissues; they adapt at a few hundredths of a second, rapid adapting. They represent 15% of the mechanoreceptors of the hand. They are important in detecting tissue vibrations. They are a myelinated afferent axon terminal surrounded by layers of lamella. They contain a lymph-like fluid inside.

Sympathetic ganglia location

located in a vertical row on either side of the vertebral column

Rods

located in retina (around 92 million), 1000 times more sensitive than cones, contain more disks in their outer segments, function to convert visual stimuli in the form of photons (particles of light) into chemical and electrical stimuli that can be processed by nervous system

Malleus location

located in the middle ear and it is connected to the eardrum.

Incus location

located in the middle ear and it is connected to the floor plate and then the oval window.

Hair cell location and function

located in the organ of corti of the cochlea. There are 15,000 of these in each of our ears. They DO NOT regenerate. Their function is to generate receptor potentials because they convert mechanical energy into electrical energy

Cones

located on central fovea (around 5 million), required for bright light and color vision, red blue and green cones

Parasympathetic ganglia location

located very close to or actually within the wall of a visceral organ

Vascular tunic (iris, ciliary body, and choroid)

mesodermal and is between the fibrous tunic and neuroectodermal tunic, oxygen supply and nutrition for eye

Optic Disk

o It is the site where the optic nerve enters the eyeball o Entry point for major blood vessels that supply the retina o Corresponds to a small blind spot in each eye because there are no rods or cones overlying the disc

Olfactory receptors

o Located in olfactory epithelium, lines the roof and sides of nasal cavity, small in area, bipolar (two projections from cell body) (first projection the dendrite which extends to surface of olfactory epithelium, second projection an unmyelinated axon)

Olfactory pathway

o Receptor cells, nerves, bulb, tract, striae, cortex, output targets of the olfactory cortex

Visual pathway

o Retina, optic nerves, optic chiasm, optic tracts, lateral geniculate bodies, optic radiations, and visual cortex

Bipolar cells

o connect inner and outer retina, receive direct synaptic input from cluster of photoreceptors, receive indirect input from surrounding photoreceptors

Ganglion cells

o located on inner surface of retina, fire action potentials whether they are exposed to light or not

Photoreceptors

o located on outermost layer of retina, hyperpolarizes in response to light and the output is sent to horizontal cells that hyperpolarize, connected to bipolar cells and horizontal cells

Fibrous tunic (cornea and sclera)

outer layer made of dense connective tissue, protects and maintains shape of eyeball

Photopigment found in rods

rhodopsin

Peripheral field

side vision, ability to see objects around without moving head or eyes

Three possibilities for synapse in the sympathetic ganglia

synapse with postganglionic neuron in the ganglion it first reaches (this is the preferred mode of travel), it may ascend or descend to a higher or lower ganglion before synapsing with postganglionic neurons at a different level or it may continue, without synapsing, through the sympathetic trunk ganglion, becomes a splanchnic nerve, and proceeds to a prevertebral (collateral) ganglion where it synapses with the postganglionic neuron.

Preganglionic Neuron

the first of two autonomic motor neurons, the cell body is located in the brain or spinal cord and they are myelinated axons, which usually extends to an autonomic ganglion where it synapses with the postganglionic neuron

Dynamic equilibrium

the maintenance of body position (mainly the head) in response to sudden movements such as rotation, acceleration and deceleration. This is accomplished by the cristae receptors.

Static equilibrium

the maintenance of posture, balance and body position (mainly the head) relative to the force of gravity. This is accomplished through macular receptors.

Postganglionic Neuron

the second neuron in the autonomic motor pathway, the cell body and dendrites are located in autonomic ganglia, where they synapse with one or more preganglionic fibers. They are non-myelinated Axon fibers of a postganglionic neuron terminates in a visceral effector organ

Fovea centralis

thinning of the retina, appears as a pit, responsible for sharp vision

Effects of sympathetic and parasympathetic divisions on various organs

view doc

Macula lutea

yellow oval spot at center of retina, responsible for sharp vision

Somatic sensory system

· Input to the nervous system is provided by sensory receptors that detect such stimuli as touch, sound, light, pain, cold, and warmth. These receptors change sensory stimuli into nerve signals and the information conveyed in these signals is then processed by the nervous system. The components of the brain interact to receive sensory input, integrate and store the information, and transmit motor responses.

General somatic senses

· The general somatic senses are touch, pressure, vibration, itch, tickle, warmth, cold and pain. They arise from receptors located in the skin as well as proprioception. · For example pressure sensitive receptors found in large muscular arteries that regulate blood pressure are baroreceptors, they are located in the aorta, carotid.

Posterior column medial lemniscus pathway

· The medial lemniscus extends from the medulla to the thalamus to the somatosensory cortex. This pathway carries discrete signals of the posterior columns of the spinal cord decussates to the medulla, it will ascend into the thalamus. · The nerve impulses for conscious proprioception and most tactile sensations ascend to the cortex along a common pathway formed by three-neuron sets. · These neurons are a part of the posterior columns which consist of the gracile fasciculus and cuneate fasciculus. 1. Impulses conducted along this pathway are concerned with fine touch, proprioception, and vibratory sensations.

How receptors are classified

· They are classified microscopically, by location and by the type of stimulus detected.

Visceral efferent pathway

· They transmit nerve impulses to three effector organs, which are glands, smooth muscle and cardiac muscle. · Two divisions that distribute visceral outflow from the CNS are: the Sympathetic (Thoracolumbar) and the parasympathetic (Craniosacral). · The visceral motor neurons regulate visceral activities by either exciting or inhibiting ongoing activities of effector organs. These two systems generally have opposing actions one stimulates the other one inhibits.

Nociceptors

· detect damage to the tissues whether physical or chemical. They are naked nerve endings located in the skin; there is a very high concentration of these in our bones. They are also located in anterior walls and joint surfaces. Most other deep tissues are not extensively supplied with pain receptors. They are stimulated and produce pain at temperatures below 10 degrees C and above 48 degrees C. They adapt very little or not at all because it allows the patient to keep being informed of the damaging stimulus and to seek treatment.