Week 5 Visual Systems

Function of sensory systems

receive information from the environment

what controls control eye movement

oculomotor (3), trochlear (4), abducens (6)

extraocular muscles

what are the 4 functions of the visual system

1. sight

2. eye movement control

3. visual perception

4. information used in postural and limb movement control (how we interact with our environment)

what is visual perception

recognition of objects and location of objects

two objectives of eye movement

keep eyes stable during head movements

direct gaze at visual targets

what are the 2 types of categories of eye movement

conjugate movements

vergence movements

direction of gaze is achieved by what?

• fast saccadic

• smooth pursuits

• vergence movements

fast saccadic

fast eye movement to switch gaze from one object to another

smooth pursuits

eye movements that follow a moving target

vergence movements

moves the eyes towards or away from a midline

gaze stabilization is achieved by what two mechanisms?

• vestibulo-ocular reflex

• optokinetic nystagmus

function of VOR

adjusts eye position during fast head movements

function of optokinetic nystagmus

adjusts eye position during slow head movements (or when objects move relative to the head)

what is another word for vestibulo- ocular reflex (VOR)

doll’s eye reflex in newborn infants

what does suppression of the VOR help

maintain voluntary control over the VOR reflex

what are the main structures of the eye (non-neural peripheral structures)

pupil, cornea, iris and the lens

what is the pupil

opening in the middle of the iris where light enters

what is the cornea

outer layer at the front of the eye, which bends and focuses the light rays

function of the iris

controls the size of the pupil to regulate the amount of light entering the eye

lens of the eye

changes in shape and fine-tunes the eye’s focus

what is the function of ciliary muscles

helps adjust the shape of the lens

what are the neural peripheral structures in the eye

retina, macula, fovea, nasal hemiretina and temporal hemiretina

retina

a thin sheet which lines the rear wall of the eyeball (located on the posterior)

macula

concave area in the retina

center part of the concave area

fovea

what is found in the fovea

the highest concentration of cones

nasal hemiretina

portion of the retina that lies medial to the fovea

temporal hemiretina

portion of the retina that lies lateral to the fovea

what are the neural structures located in the retina

photoreceptors (rods and cones)

bipolar cells

ganglion cells

optic nerve

optic disk

what’s the function of rods

detect dim light

what is the function of cones

acuity and detect color

function of photoreceptors

transduce light into electrical signals

bipolar cells do what

link photoreceptors to ganglion cells

collect visual signals from photoreceptors (rods and cones) and relay them to retinal ganglion cells

what is the output neuron of the eye

the ganglion cells in the retina

where in the retina does the action potential get generated?

the ganglion cells

optic nerve

axons join together to exit the retina

the optic disk

blindspot area with no photoreceptors

what are the 4 main steps of the central visual pathway

1. retina covers light into neural cells

2. signals processed within the retina and are conveyed to the retinal output cells

3. first project neuron: transmits signals from the retina to the thalamus

4. second project neuron: transmits signals from the thalamus to the primary visual cortex

function of the optic nerve

carries info from both visual fields (only select fibers cross the optic nerve)

function of the optic chasm

where the optic nerves (one from each eye) come together and cross

function of the optic tract

conveys visual information from the chasm to the lateral geniculate nucleus of the thalamus

what are the 2 subcortical projects in the optic tract

the lateral geniculate nucleus and the superior colliculi

optic radiations

emerge from the lateral geniculate nucleus and project to the primary visual cortex

primary visual cortex does what?

discriminates shape, size, texture of objects

function of secondary visual areas

analyzes for colors and motions

what is the dorsal/action stream

information is used to direct movement

ventral system/perception stream

information is used to recognize visual objects - what is it? helping to identify objects

visual field

the amount of world that can be seen at a point of time, without head or eye movements

lesion of the optic nerve

total loss of vision in the ipsilateral eye (blindness in one eye)

lesion to the optic chiasm result

bitemporal heminaopia

interrupts fibers from both nasal hemiretinas (AKA tunnel vision)

lesion to the optic tract, LGN, optic radiation result

contralateral homonymous hemianopia

loss of contralateral visual field (opposite side visual field)

lesion to the visual cortex

contralateral homonymous hemianopsia (lose ½ of visual field)

possible macular sparing

age related macular degeneration (etiology, pathology, symptoms, prognosis)

etiology: age related

pathology: photoreceptor loss in macula

symptoms: central vision impaired, blurriness, object distortion (wavy objects)

prognosis: progressive

somatosensation

information about state of body (skin, musculoskeletal system, visceral organs)

what are the 3 main functions of somatosensory info

1. exteroception

2. proprioception

3. interoception

what is exteroception

• one of main functions of somatosensory info

• sense of direct interactions with the external world and its impact on the body

proprioception

• one of main functions of somatosensory info

• sense of one’s own body, involving sensations from muscles, joints and tendons

interoception

• one of main functions of somatosensory info

• sense of the functions and state of internal body organs (from our own body)

what are the two main general tactile system functions

1. discriminative touch/tactile perception

2. social/affective touch

function of the discriminative touch/tactile perception

• detection and perception of objects and materials that contact skin

• contributes to development of body schema and praxis

• associated with fine motor coordination

function of the social/affective touch

• light, caressing touch

• emotional bonding: contact and comfort

• emotion and arousal regulation

function of proprioception (3)

• provides a continuous flow of sensation from the muscles, joints and tendons

  • detection of joint position and movement

  • spatial orientation of the body/body parts

  • amount of force our muscles are exerting

tactile (5 function/purposes)

• physical safety

• connection from the social world

• exploration of the environment

• development of body scheme and motor skills

• influence on state regulation (arousal and activation)

proprioception

• physical safety

• development of motor skills and motor learning

• refinement of movement

• timing of movement

• influence on state regulation (arousal and activation)

what are the two types of receptors in somatosensation

cutaneous receptors, proprioceptors

cutaneous receptors

all cutaneous receptors are stimulated by physical deformation of the receptor itself or the surrounding area

proprioceptors

specialized mechanoreceptors located in the muscles, tendon, joints and vestibular apparatus of the inner ear

what are the 5 types of somatosensory receptors

1. touch

2. body part position and movement

3. temperature

4. chemicals

5. pain

touch receptors respond to what?

mechanical deformation of receptor

mechanoreceptors

respond to length of muscle, tension of joints and tendons, etc

thermoreceptors

responds to heat or cooling

chemoreceptors

responds to substances released by cells

nociceptors

sensitive to stimuli that damage or can damage

what are the 2 types of receptor adaptations

1. slow adapting/tonic

2. fast adapting/phasic

slow adapting/tonic

receptor continues to fire during entire presentation of the stimulus

fast adapting/phasic

receptor adapts quickly to stimulus and stops responding (phasic receptors)

receptive field

area of skin innervated by a single afferent neuron

large receptive field

borders are difficult to define; often cover a large area

small receptive field

borders are sharply defined; covers small area

meissner’s corpuscle

light tough and vibration, phasic

merkel’s disk

pressure; tonic

pacinian corpuscle

vibration and touch; phasic

Ruffini corpuscle/ending

skin stretch; tonic

crude/coarse touch

free nerve endings: pressure, tickle/itch

muscle spindle

around muscle fibers in muscle belly

Golgi tendon organ

in junction between muscle fiber and tendon (muscle to bone)

what are the three types of sensory pathways

• conscious relay pathway

• divergent pathways

• unconscious pathways

conscious relay pathway

info about location and type of stimulation to cortex

divergent pathways

transmit info to many areas of the brainstem and cerebrum

unconscious pathways

brings unconscious proprioceptive and other movement- related information to the cerebellum

what are the 3 primary components of the somatosensory pathways

1. receptors

2. sensory pathways

3. brain centers

primary afferent fiber

first order neurons are psuedounipolar

dorsal horn- white or gray matter?

gray matter (h)

dorsal column- white or gray matter?

white matter

dermatomes

area of skin innervated by axons from cell bodies in a single dorsal root