APII exam 1

Afferent Division of the Nervous System

Receptors – detects stimuli. Sensory neurons – relays sensory information towards the CNS (receives input from dendrites, uses axon to send it to CNS). Sensory pathways – nerves, nuclei, and tracts that deliver sensory information to the CNS

Efferent Division of the Nervous System

Nuclei – contain cell bodies of motor neurons.

Motor neurons – send commands to effectors through motor tracts (axons in the CNS) or nerves (axons in the PNS)

Sensation

The arriving information from these senses

Perception

Conscious awareness of a sensation. Interpretation of electrical signals. Ex. Awake brain surgery

Nuclei

cluster of cells located in the cns

Nerves

bundle of axons in the pns

Tracts

bundle of axons in the cns

Somatic nervous system

motor neurons and pathways that provide voluntary control of skeletal muscles

General senses

Distributed throughout the body. Includes: temperature, pain, touch, pressure, vibration, and proprioception.

Propriception

monitors the position and movement of skeletal muscles. Spacial awareness, 3D perception of body position.

Receptor specificity

each receptor has a characteristics sensitivity. Ex: your hands can smell, but can perceive touch sensations.

Receptive field

Area monitored by a single receptor cell. The larger the receptive field, the more difficult to locate stimulus.

Special senses

sensory receptors are all located in the head and surrounded by protective tissue. Includes: olfaction, vision, gustation, equilibrium, hearing.

Interpretation of sensory information

\-Arriving stimulus reaches cortical neurons via labeled line (link between the receptor and cortical neuron).

\-Each labeled line consists of axons carrying info about one type of stimulus (modality)

\-Shares info with specific neurons, each have own axon.

Adaption

* The frequency and pattern of action potentials contain information about the strength, duration, and variation of the stimulus
* reduction in sensitivity of a constant stimulus
* your nervous system quickly adapts to stimuli that are painless and constant

Central Adaption

* inhibition of the nuclei along sensory pathway (occurs in CNS)
* Ex: new smells still stimulate sensory receptor, but cortical neurons no longer respond to the stimulation

Peripheral Adaption

* Occurs at the level of the receptor (receptor responds initially then stops)
* thermometers (ex. adapt to hot tub then jump in pool)

Tonic Receptors

* are always active
* show little peripheral adaption
* are slow adapting receptors
* remind you of an injury long after the initial damage
* Action potentials are generated at a frequency that reflects the backgroud level of stimulation when the stimulus increases or decreases, the rate of action potential generation changes accordingly
* Ex: pain receptors (nociceptors)

Phasic Receptors

* are normally inactive
* become active for short period of time when a change occurs
* are fast adapting receptor
* provide information about the intensity and rate of change of stimulus
* Ex: thermorecptors detect rapid changes in temperature
* stimulation of a receptor produces action potential (along the axon of a sensory neuron)
* The frequency and pattern of action potentials contain information (about the strength, duration, and variation of the stimulus)
* Your perception of the nature of that stimulus (depends on the path it takes inside the CNS)

\

Classifying Sensory Receptors: Exteroceptors

Provide information nabout the external environment

Classifying Sensory Receptors: Proprioceptors

Report the positions of skeletal muscles and joints, purely somatic sensations. None in visceral organs

Classifying Sensory Receptors: Interoceptors

Monitor visceral organs and functions

General Sensory Receptors: Nociceptors

* pain
* are common
* in joint capsules
* within periostea
* around the walls of blood vessels
* are free nerve endings with large receptive fields
* not protected by accessory structure
* Type A and C fibers

Nociceptors Sensitivities

* temperature changes
* mechanical damage
* dissolved chemicals, such as chemicals released by injured cells

Type A fibers

* carry sensations of fat pain such as that caused by an injection or deep cut
* sensations reach the CNS quickly and trigger somatic reflexes
* sensations relayed to the primary sensory cortex and receive conscious attention
* withdrawal reflex

Type C fibers

* carry sensations of slow pain, burning and aching pain
* cause a generalized activation of the reticular formation and thalamus
* aware of pain but only general idea of affected area

General Sensory Receptors: Thermorecptors

* also called temperature receptors
* are free nerve ending located in teh hypothalamus, dermis, skeletal muscles, and liver
* conducted along the same pathways that carry pain sensations
* sent to: reticular formations, thalamus, and primary sensory cortex (less)

General Sensory Receptors: Mechanoreceptors

* sensitive to stimuli that distort their plasma membrane
* contain mechanically gated ion channels whose gates open in response to: tactile touch, pressure, vibration, stretching, compression, and twisting
* \

3 classes of mechanorecptors: Tactile Receptors

* provide the sensations of touch, pressure, and vibration
* touch sensations provide shape and texture
* pressure sensations indicate degree of mechanical distortions
* vibration sensation indicate pulsing or oscillating

3 classes of mechanorecptors: Barorecptors

detect pressure changes in the walls of blood vessels and in portions of the digestive, respiratory, and urinary tracts

3 classes of mechanorecptors: Proprioceptors

* monitor the positions of joints and muscles
* the most structurally and functionally complex of general sensory receptors
* 3 Major groups:
* 1. Muscles spindles (monitor muscle length and trigger stretch reflexes)
* 2. Golgi tendons (stimulated by tension in tendon, between muscle and tendon, monitor external tension developed during contraction)
* 3. Receptors in joint capsules ( free nerve detect pressure, tension, movement at the joint)

Types of Tactile Receptors: Free nerve endings

* sensitive to touch and pressure
* situated between epidermal cells
* free nerve endings providing touch sensations are tonic receptors (slow adapting) with small receptive fields

Types of Tactile Receptors: Root hair plexus

* monitor distortions and movements across the body surface wherever hairs are located
* Phasic (fast adapting), best at detecting initial contact and subsequent movements

Types of Tactile Receptors: Tactile discs

* also called merkel discs
* fine touch and pressure receptors
* extremely sensitive tonic receptors (slow adapting)
* have small receptive fields

Types of Tactile Receptors: Tactile corpuscles

* also called Meissner’s corpuscles
* perceive sensations of fine touch, pressure and low frequency vibration
* Phasic, adapts within 1 second after contact
* karge structures
* most abundant in the eyelids, lips, fingertips, nipples, and external genitalia

Types of Tactile Receptors: Lamellated Corpuscle

* also called pacian corpuscles
* sensitive to deep pressure
* phasic (fast adapting)
* most sensitive to pulsing ot high frequency vibrating stimulus

Types of Tactile Receptors: Ruffini Corpuscles

* also sensitive to pressure and distortion of the skin
* located in the reticular (deep) dermis
* tonic (slow adapting)

General Sensory Receptors: Chemorecptors

* respond only water-soluble and lipid soluble substances dissolved in surrounding fluid
* receptors exhibit peripheral adaption over period of seconds (central adaption may also occur
* receptors that monitor pH, carbon dioxide, and oxygen levels in arterial blood are located in:
* Carotid bodies- Near the origin of the internal carotid arteries on each side of the neck
* Aortic Bodies- between the major branches of the aortic area

first order neuron

* sensory neuron delivers sensations to the CNS
* cell body of a first-order general sensory neuron is located in dorsal root ganglion or cranial nerve ganglion

second order neuron

* Axon of the sensory neuron synapses on an interneuron in the CNS
* may be located in the spinal cord or brain stem

third order neuron

* if the sensation is to reach our awareness, the second order neuron synapses on a third order neuron in the thalamus

Somatic Sensory Pathways: Spinothalamic pathway

* provides conscious sensations of poorly localized (crude) touch, pressure, pain, and temperature
* First order neurons
* axons of first order sensory neurons enter spinal cord and synapse on second-order neurons with posterior grey horns
* second order neurons
* cross to the **opposite side** of the spinal cord before ascending up the spinal cord
* ascend within the anterior (crude touch/pressure) or lateral (pain/temp) spinothalamic tracts
* Third order neurons
* synapses in ventral nucleus of the **thalamus**
* after sensations have been sorted and processes they are relayed to the **primary sensory cortex**

Referred Pain

* the pain of a heart attack is frequently first felt in the left arm
* the pain of appendicitis is generally felt first around the navel and then in the right lower quadrant

Somatic Sensory Pathways: Posterior Column Pathway

* Sensory homunculus- functional map of the primary sensory cortex
* distortions occur because area of sensory cortex devoted to particular body region is not proportion to regions size, but to number of sensory receptors it contains

Somatic Sensory Pathways: Spinocerebellar pathway

* cerebellum receives **proprioceptive** information about position of skeletal muscles, tendons and joints

Thalamus

site of sensory information processing (except for smell)

General Pattern of sensory processing

* spinal and cranial reflexes provide rapid, involuntary, **preprogrammed**, responses that perserve **homeostasis** over short term
* cranial and spinal reflexes control the most basic motor activities

Amyotrophic Lateral Sclerosis (ASL)

* **progressive** degenerative disorder affecting **motor neurons** in the spinal cord, brain stem, and cerebral hemisphere.
* Death of motor neurons causes **atrophy** in associated skeletal muscles
* Cause: 5-10% inherited, rest unknown
* Treatment: oral medications such as riluzole mitigate symptoms but cannot reverse damage

Cerebral Palsy (CP)

* number of disorders affecting voluntary motor control, motor skills, posture, balance, memory, speech, and learning
* dysfunction is **not progressive.** Can appear during infancy or childhood and persist through entire life
* possible causes: unusually stressful birth, maternal exposure to drugs, genetic defect affecting motor pathway development
* Treatment: medication (muscle relaxants and pain relievers) and therapy (OT/PT, speech).

Senses dependent in Chemoreceptors

olfaction and gustation

Senses dependent on mechanoreceptors

equilibrium and hearing

Olfactory organs

* provide sense of smell
* made up of two layers
* wet inside
* hard to smell when dry

\

olfactory epithelium

contains receptor cells, **basal (stem) cells** to replace olfactory glands that die off

Lamina Propria

contains areolar connective tissue blood vessels, nerves, olfactory glands (produce mucus)

olfactory pathways

* axons leaving olfactoty epithelium collected into 20 or more **bundles**
* penetrate **cribiform plate** of ethmoid bone
* reach **olfactory bulbs** of cerebrum where first synapse occurs
* axons leaving the **olfactory tract travel** along olfactory tract to reach olfactory cortex, **hypothalamus,** and portions of **limbic system**
* arrive at information centers without going through __thalamus__

olfactory discrimination

* can distinguish thousands of chemical stimuli
* CNS interprets smell by the pattern of receptor activity

olfactory receptor population

declines with age

Taste receptors

* are distinguished on tongue and portions of pharynx and larynx
* clustered into taste buds
* associated with epithelial projections (lingual papillae) on superior surface of tongue

4 types of Lingual Papillae

1. Filiform papillae


1. __Do Not__ contain taste buds
2. provide friction
2. Fungifrom papillae


1. contain about 5 taste buds each
3. Vallate Papillae


1. contain 100 taste buds each
4. Foliate papillae


1. folds located at lateral margins of tongue

Taste buds contain:

* basal (stem) cells
* gustatory receptor cells
* extend taste hairs through the taste pore
* Monitored by cranial nerves VII (facial), IX (glossopharyngeal), and X (vagus) that synapse onto neurons within the **medulla oblongata** from there axons head to **thalamus** and primary sensory cortex

4 Primary taste sensation

1. sweet
2. salty
3. sour
4. bitter

Umami

* characteristics of beef/chicken broths and Parmesan cheese
* receptors sensory to amino acids, small peptides, and nucleotides

Fat

* **Long Chain Fatty Acids (LCFA)** have specific receptors in taste buds
* may be the sixth taste modality

water

detected by water receptors in the pharynx

salt and sour receptors

* use passive/leak channels (Na+ or H+ enter through the Na+ leal channels)
* stimulation produces depolarization of cell
* 1,000 times more sensitive to acids (sour taste) than sweet/salty

sweet, bitter, and umami stimuli

* activate g proteins- **Gusducins**
* acts like order detectant
* 100,000 times more sensitive to bitter than acids bc bitter for foods are slightly toxic to us
* alter pH in blood

Phenylthiocarbamide (PTC)

70% of Caucasians can taste it, inherited

age and taste

number of taste buds declines with age

Palpebrae

* eyelids
* continuation of skin
* blinking keeps surface of eye lubricated and free of dust & debris

Tarsal glands

secrete **lipid rich** product that helps keep eyelids from sticking together

Lacrimal carnucle

* located laterally
* mass of soft tissue containing glands producing thick secretions
* contributes to **gritty deposists** that appear after a goodnights sleep

Conjuntiva

epithelium covering inner surface of eyelids (**palpebral conjunctive**) and other surfaces of eye (**ocular conjunctiva)**

Conjunctivitis (pink eye)

inflammation/ redness caused by allergy, chemical irritation, or pathogenic infection

Lacrimal apparatus

produces, distributes, and removes tears

Lacrimal gland

* tear gland
* located laterally
* watery secretions contain lysozyme, and antibacterial enzyme, and antibodies. Slightly alkaline (basic, a little above pH 7)

eyeball

* hollow but not empty
* is divided into two cavities by the lens
* large posterior/ vireous cavity- filled with vitreous humor
* small anterior cavity- filled with aqueous humor
* consits of the anterior chamber (anterior to iris) and posterior chamber (posterior to iris)

Fibrous Layer

* sclera (white of eye)
* cornea (transparent anterior region)
* Corneal limbus (border between cornea and sclera)

Vascular Layer (Uvea) Functions

* Provides route for blood vessels and lymphatics that supply tissues of eye
* regulates amount of light entering eye
* secretes and reabsorbs **aqueous humor** that circulates within chambers of eye
* controls shape of the **lens**, which is essential to focusing
* adjusts size of lens

Vascular Layer (Uvea) Components

* **Iris-** contains papillary muscle
* change diameter of **pupil**
* sympathetic and parasympathetic innervation changes the diameter of pupil by stimulating the **pupillary dilator** (outside ring, radiate toward pupil, sympathetic) or the **pupillary constrictor** (inside ring, parasympathetic)
* **Ciliary Body**- contains ciliary processes and ciliary muscle that attaches to suspensory ligaments of lens
* controls position and shape
* **Choroid**- Delivers oxygen and nutrients to retina

Inner Layer

* outer layer called pigmented part, absorbs light
* inner called neural part (**retina**)
* contains visual receptors and associated neurons
* has rods and cones which are **photoreceptors**
* the inner neural part has:
* bipolar cells
* neurons of rods and cones synapse with **ganglion cells** by connecting to bipolar cells first
* horizontal cells
* extend across outer outer portion of retina
* where photoreceptors synapse with bipolar cells
* amacrine cells
* comparable to horizontal cell layer
* where bipolar cell synapse with ganglion cells

Rods

* do not discriminate light colors
* highly sensitive to light-- __used in low light (night)__

Cones

* stimulated by light
* provide color vision
* densley clustered in **fovea centralis**, at center of **macula**

optic disc

* each eye has its own optic disc and blind spot
* has a **blind spot** because it is the origin of the optic nerve

Scotomas

* Abnormal blind spots (located in areas other than optic disc).
* May be caused by compression of optic disc, damage to photoreceptors, damage to visual pathways

Chambers of the eye

the smaller anterior cavity is divided into two chambers by the iris

* anterior chamber
* extends from cornea to iris
* posterior chamber
* between iris, ciliary body, and lens

Aqueous humor

* fluid that circulates within the eye
* diffuse through walls of anterior chamber into **scleral venous sinus** (canal of schlemm) before re-entering blood circulation
* diffusion relieves pressure
* **intraocular pressure**- fluid pressure in aqueous humor
* helps retain eye shape

Glaucoma

decreased aqueous humor drainage causes increase in pressure. Compresses optic nerve affecting peripheral vision first

Diabetic Retinopathy

* develops in many with diabetes mellitus
* visual activity decreases as photorecptors die
* caused by blockage of normal blood vessels in retina,or blood leakage into cavity

detached retina

* may be caused by sudden hard impact, detaches retina from pigmented part. Attached together by laser welding two layers- causes blind spots. If not treated will degenerate

Cataract

* condition in which lens has lost its transparency
* senile cataract- most common type, consequence of aging process

Astigmatism

* condition where light passing through the cornea and lens is not refracted properly
* abnormal shape
* visual image is distorted
* corrected with glasses/contacts

Ciliary muscle

* when it __contracts__ the lens __thickens__ and images of __nearby__ objects focused onto retina
* when it __relaxes__ the lens __flattens__ (thins) and images of __far away__ objects focused onto retina

emmetropia

normal vision

myopia

nearsighted (distant objects blurry)

hyperopia

farsighted (near objects blurry)

Photopigments

* absorb light energy
* synthesized from vitamin A

Retinitis Pigmentosa

* most common __inherited__ visual problem
* caused by mutation in visual pigment
* results in photoreceptor cell death and blindness

Color blindness

* inability to detect certain colors
* cones might be missing or present but unable to produce visual pigments to absorb light of that frequency
* more common in men

Nyctalopia

* night blindness
* can result from deficiency of vitamin A

central processing of visual information

* axons from ganglion cell converge on optic disc
* penetrate wall of eye
* proceed toward diencephalon as optic nerve (II)
* two optic nerves (one for each eye) reach diencephalon at **optic chiasm** - then becomes **optic tract**
* half the fibers travel to the contralateral **lateral geniculate nucleus**, the other half to the ipsilateral side