last lecture

spinal cord location

Begins at the foramen magnum, ends at L1 or L2 vertebra

spinal cord functions

Provides two-way communication to and from brain, contains spinal reflex centers

Spinal Cord Anatomy

cervical and lumbar enlargements
Conus medullaris: cone shaped inferior taping of the spinal cord
Film terminale:thin fibre like extensions of the pia mater
Cauda equine: collection of nerve roots at caudal (tail) end
31 pairs of spinal nerves

31 pairs of spinal nerves

8 cervical (C1-C8)
12 thoracic (T1-T12)
5 lumbar (L1-L5)
5 sacral (S1-S5)
1 coccygeal (Co1)

spinal nerve is formed by

union of dorsal and ventral root

Ventral rami

Spinal nerve, forms a complex of networks (plexus) for the anterior

Dorsal rami

branch of spinal nerve that supplies nerves to muscle of the back and the skin

Cervical Nerves (C1-C4)

muscles and skin of neck and shoulder

C5-T1

Brachial nerve shoulder, upper limb and some thorax

Lumbar (L1-L4) plexus

anterior and medial thigh muscles cutaneous supply to anterior thigh and part of leg

Sacral (L5-S4)

Lower Leg

12 nerves

Olfactory sensory,
Optic sensory,
Oculomotor motor,
Trochlear motor,
Trigeminal mixed,
Abducens motor,
Facial mixed,
Vestibulochlear sensory,
Glossopharyngeal mixed,
Vagus mixed,
Accessory Motor,
Hypoglossal motor

eyes

located in orbits, only one sixth of the surface of eye is visible from outside

Eyelids (palpebrae)

Two movable flaps of skin which cover and uncover each eyeball. protects the eye from excessive light, and spread lubricating substances over the eyeball.

Palpabral Fissure

space between eyelids

median angle (canthus)

corner of the eye where the upper and lower eyelids meet, has fleshy reddish elevation called caruncle containing glands,

Eyelashes function

first line of defense for your eyes, keeping airborne dirt, dust, lint and other debris from reaching the delicate eye tissues

meibomian glands

oil glands found in the upper and lower edges of the eyelids that help lubricate the eye

sebacous collar glands

in hair follicles, infection causes sty

conjunctiva

mucous membrane lining the eyelids and covering the anterior portion of the sclera

palpebral conjunctiva

membrane that lines underside of eyelids

Conjunctivitis

inflammation of the conjunctiva (pink eye)

Vitamin A

necessary for conjunctiva and for retina

lacrimal apparatus

the structures that produce, store, and remove tears

lacrimal ducts

tubes that carry tears to the lacrimal sac

parasympathetic stimulation

causes tears during emotions

extrinsic eye muscles

Six muscles attach to the outer surface of the eye and produce eye movements, superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, inferior oblique

strabismus

crossed eyes or squint

diplopia

double vision

fibrous tunic

outer layer of the eye, sclera and cornea

vascular tunic (uvea)

middle layer of the eyeball composed of the choroid, ciliary body, and iris

sensory tunic (retina)

pigmented layer and neural layer

pathway of light through retina

cornea, aqueous humor, lens, vitreous humor, photoreceptors in retina

How do we see different colors?

when the 3 types of cone cells are stimulated in different proportions you see different colours

Refraction

The bending of a light wave as it passes at an angle from one medium to another

Convex lenses

bulge outside, They converge the light rays so the focal point moves closer.

Concave lenses

cave inwards. They diverge the light rays so the focal point moves farther.

accomodation of lens

lenses change shape to focus on objects near or far, by contraction of ciliary muscles

near point of vision

the closest an object can be and still come into focus

constriction of pupil

Pupil gets smaller, blocks peripheral light rays and reduces spherical aberration (blurry edges)

convergence of eyeballs

medial rotation of the eyeballs toward the object being viewed, cross-eye condition if the object is very close.

Myopia (nearsightedness)

occurs when the image is focused in front of the retina

Hypermetropia (farsightedness)

Can see distant objects normally but problem in near objects
Due to short eyeball and inadequate refractory power of the lens.

emmetropia

normal vision

astigmatism

a condition in which the eye does not focus properly because of uneven curvatures of the cornea

presbyopia

lens elasticity is impaired as a result of old age

Photoreception

process by which the eye detects light energy

Two types of cells in the retina convert light energy into electrochemical signals that reach the brain via optic nerve

Rod cells and cone cells

Rods

retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones don't respond

Cones

are for vision in bright light and for color vision and acuity.
Only one or a few cones to a ganglion cell.

Rods and cones contain

photopigments necessary for the absorption of light

Photopigment molecules have two parts

Retinal and opsin

retinal

Light-absorbing molecule, Retinal is derived from Vitamin A which is stored in pigment layer cells of retina and in the liver.

Opsin

a class of protein that, together with retinal, constitutes the photopigments. Scotopsin in rods and Photopsin in cones.

three primary colors

blue, green, red

color blindness

a variety of disorders marked by inability to distinguish some or all colors

red-green color blindness is more common; more in males -why?

because the genes responsible for the most common, inherited color blindness are on the X chromosome. Males only have one X chromosome, while females have two X chromosomes.

light and dark adaptation

The process by which the eyes become more sensitive to light in the dark and less sensitive to light, in the light. : Rhodopsin is amazingly sensitive to light; it gets easily bleached in bright light but is quickly regenerated in dim light.

rhodopsin

A light-sensitive pigment found in the rod cells that is formed by retinal and opsin.

nyctalopia

night blindness

binocular vision

the ability to focus the two eyes in a coordinated manner in order to see one image

Glaucoma

aqueous humor drainage is impaired

cataract

clouding of the lens of the eye

three areas of the ear

outer, middle, inner

external ear

pinna or auricle collects sound waves,

External auditory canal (meatus) directs sound waves to the ear
drum,

ceruminous or wax glands (modified sweat gland) which secrete cerumen

Cerumen (ear wax) function

Protects ear canal from drying out,
prevents the invasion of insects and other foreign bodies.
keeps the outer surface of the eardrum pliable,
waterproofs and blocks entry of foreign material.

tympanic membrane

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

middle ear

the chamber between the eardrum and cochlea containing three tiny bones (hammer, anvil, and stirrup) that concentrate the vibrations of the eardrum on the cochlea's oval window

middle ear cavity (tympanic cavity)

Tympanic cavity which is connected to the nasopharynx by eustachian tube or auditory tube.

auditory tube (eustachian tube)

equalize pressure

otitis media

inflammation of the middle ear

mastoid antrum

Canal for communication with mastoid air cells

ear popping

is to equalize pressure on the two sides of ear drum.

Three tiny middle ear bones

malleus (hammer shaped),
incus (anvil shaped), and
stapes (stirrup shaped)

middle ear bones function

Amplify and transmit sound from eardrum to oval window/inner ear

two middle ear muscles

tensor tympani and stapedius

tensor tympani

the muscle attached to the malleus; tensing the tensor tympani decreases vibration

stapedius

the muscle attached to the stapes; tensing the stapedius decreases vibration

inner ear (labyrinth)

It is also called labyrinth and has two parts
bony or osseous labyrinth which contains a fluid perilymph,
membranous labyrinth contains endolymph

three parts of the bony labyrinth

vestibule -connects to oval window,
semicircular canals - anterior, posterior and lateral
cochlea- is anterior to vestibule, coiled 2 1/2 turns, contains
three cavities

three parts of membranous labyrinth

VESTIBULE which has two parts: smaller saccule and larger utricle
Each contains a sensory structure called macula for static
equilibrium

SEMICIRCULAR DUCTS three, each with a swollen part ampulla
containing a sensory structure called crista for dynamic equilibrium

COCHLEAR DUCT present in the central cavity of cochlea.

Cochlear cavaties

scala vestibuli, scala media, and scala tympani.
Scala media contains endolymph, others contain perilymph

cochlear membranes

vestibular membrane, basilar membrane and tectorial membrane.

Basilar membrane supports organ of Corti which has sensory
receptors for hearing.

modiolus

intersection of facial muscles; provides stability for mouth movement and facial expression. Bony core of the cochlea

helicotrema

an opening in the partitioning membranes at the apex of the cochlea; provides an open pathway for the perilymph to carry vibrations through the cochlea

speed of light

186,000 miles per second

soundwaves

Travel at 0.2 miles/second

The pathway of sound waves

1) Sound waves vibrate the tympanic membrane
2) Auditory ossicles vibrate. Pressure is amplified
3) Pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli
4a) Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells
4b) Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells

How do the sound waves reach from outside to the organ of Corti

Sound waves enter the ear via the auditory canal and cause vibration of the tympanic membrane. Movement of the tympanic membrane causes subsequent vibrations within the ossicles, the three bones of the middle ear, which transfers the energy to the cochlea through the oval window.

What are the functions of various parts of the ear in hearing?

Your inner ear has three main parts: your cochlea, semi-circular canals (labyrinth) and your vestibule. Your cochlea supports your hearing and your vestibule and semi-circular canals support your balance

units of measurement

Hertz or Hz for short

Normal range for human ear

20 to 20,000 Hz but our ears are more sensitive to sound waves of frequency between 1,500 to 4,000 Hz

Frequency determines pitch of sound

higher the frequency \= higher the pitch

Amplitude

Height of a sound wave, Amplitude determines LOUDNESS (intensity) of sound

Amplitude unit of measurement

DB\=Decibels
Normal range for human ear \= 0 to 120 dB

Conduction deafness

An inability to hear resulting from damage to structures of the middle or inner ear.

sensorineural deafness

deafness that results from damage to the auditory nerve. Damage to organ of corti

Tinitus

ringing in the ears

Meniere's syndrome

a rare chronic disease in which the amount of fluid in the inner ear increases intermittently, producing attacks of vertigo, nausea, vomiting and very disturbed balance.

Frequency

the number of complete wavelengths that pass a point in a given time