Anatomy Unit 3

Spinal cord functions

Spinal cord functions

1. a pathway for sensory and motor impulses

2. responsible for reflexes

Spinal cord gray matter

centrally located resembling butterfly

Gray matter subdivisions

1. anterior horns

2. posterior horns

3. lateral horns

4. gray commissure

Anterior horns

house cell bodies of somatic motor neurons in skeletal muscle

Lateral horns

contain cell bodies of autonomic motor neurons in cardiac and smooth muscle and glands

Posterior horns

contain axons of sensory neurons and cell bodies of interneurons

Sensory nuclei

within the posterior horns containing somatic and visceral

Motor nuclei

within the anterior horns containing somatic motor nuclei

Autonomic motor nuclei

found within the lateral horns

Anterior root

contains motor axons only that arise in the anterior and lateral horns of spinal cord

Posterior root

contains sensory axons only that arise in the posterior root ganglion

Spinal nerve

formed by each anterior and its corresponding posterior root that unite within the intervertebral foramen

Posterior (dorsal) ramus

smaller of the 2 main branches and innervates the deep muscles and the skin of the back

Anterior (ventral) ramus

larger of the 2 main branches and innervates the trunk and the upper and lower limbs

Nerve plexuses

network of intersecting nerves formed by anterior rami

Rami communicates

branch of the anterior ramus that extends between the spinal nerve and sympathetic trunk ganglion

Reflexes

rapid, automatic, involuntary reactions of muscles or glands to a stimulus

Rapid response

requires few neurons to be involved and synaptic delay may be minimal

Involuntary response

requires no intent or pre-awareness of the reflex activity

Reflex arc

the neural wiring of a single reflex that always begins in the PNS and ends at a peripheral effector

Autonomic nervous system (ANS)

complex system of nerves that govern involuntary actions

Somatic nervous system (SNS)

works with the ANS to regulate body organs and maintain internal functions

Visceral motor system

an autonomic motor that controls glands, cardiac muscles and smooth muscles

Parasympathetic system (craniosacral division)

rest-and-digest

calming effect on body functions

SLUDD - salivation, lacrimation, urination, digestion, defecation

Sympathetic system (thoracolumbar division)

fight-or-flight

increases alertness and reduces blood flow to skin and digestive tract

E activities - exercise, excitement, emergency, embarrassment

Autonomic tone

background level of activity created by sympathetic and parasympathetic systems functioning simultaneously

Parasympathetic tone

maintains smooth muscle tone in intestines and holds resting heart rate down at 70-80 beats/min

Sympathetic tone

maintains blood pressure by keeping vessels partially restricted

Differences between parasympathetic and sympathetic neurons

1. Preganglionic axon length

2. Postganglionic axon length

3. Autonomic ganglion location

4. Postganglionic axon neurotransmitter release

   1. ACh = Parasympathetic

   2. ACh or NE = Sympathetic

Sensation

conscious awareness to stimuli/sensory information

General receptors

temperature, pain, touch, stretch, and pressure

distributed throughout skin and organs

Special receptors

gustation(taste), olfaction(smell), vision, equilibrium, and audition(hearing)

housed in complex organs in the head

Receptors

structures that receive stimuli in either external or internal body

Exteroceptors

found in skin or mucous membranes such as nasal and oral cavities, vagina, and anal canal

Interceptors

-found in the walls of viscera; detecting stretching, oxygen depravation, temperature, and pressure

Proprioceptors

found in muscles, tendons and joints; detecting body and limb movement, muscles contraction/stretching

Somatic sensory receptors

found within the body wall; they include receptors for chemicals, temperature, pain, touch, proprioception, and pressure

Visceral sensory receptors

found within the walls of the viscera; they respond to chemicals, temperature, and pressure

Special sense receptors

located only in the head

Chemoreceptors

detect specific dissolved chemicals

Thermoreceptors

detect changes in temperature

Photoreceptors

detect changes in light, color, or movement

Mechanoreceptors

react to touch, pressure, temp, and vibration stimuli

most numerous type of receptor

located in the dermis and subcutaneous layer of the skin

Gustatory cells

taste receptors housed in taste buds which are located on the dorsal surface of the tongue

Basal cells

stem cells

Gustatory microvillus (taste hair)

dendritic ending of each gustatory cell that extends through the taste pore

activated by taste molecules within the oral cavity

Olfactory epithelium

consists of olfactory receptor cells, supporting cells, and basal cells

Olfactory hairs

nerve endings at the apical end of olfactory receptors that project through the mucous covering the olfactory epithelium

Eye

spherical organ that is 2.5 centimeters in diameter

Fibrous tunic

contains cornea and sclera

Cornea

anterior part of eye, transparent, avascular

Sclera

makes up the majority of the fibrous tunic; considered the “white” of the eye and allows for the attachment of the extrinsic eye muscles to the eye

Vascular tunic

contains choroid, ciliary body, and iris

Choroid

contains a vast network of capillaries, which supply nutrients and oxygen to the retina

Ciliary body

composed of ciliary muscles and ciliary processes; ciliary muscles contract or relax shaping of the lens to focus incoming light onto the retina

Iris

pigmented part of the eye. Black hole is called the pupil, which allows light to pass on to the retina

Retina

contains pigmented layer attached to the choroid that absorbs light energy and the neural layer that houses photoreceptors and their neurons

Fovea Centralis

area of retina that contains the highest proportion of cones and almost no rods

sharpest area of vision

Optic disc

“blind spot” on retina

located where ganglion cell axons exit retina to form optic nerve

lacks photoreceptors

Anterior cavity of eye

between the lens and cornea and contains aqueous humour

Posterior cavity of eye

posterior to the lens and anterior to the retina and contains vitreous humour

Photoreceptor layer

outermost layer of neural layer composed or rods and cones

Bipolar cells

synapse with photoreceptors and ganglion cells of the neural layer

Ganglion cells

innermost layer of the retina

axons of these cells leave the retina and form the optic nerve

Auricle

skin covered, funnel-shaped, elastic cartilage supported structure of the outer ear

External acoustic meatus

bony tube located off of the auricle that ends at the tympanic membrane

Cerumen

a wax-like secretions produced by glands deep within the external auditory meatus

Middle ear

air-filled tympanic cavity just medial to the tympanic membrane

Malleus

auditory ossicles attached to tympanic membrane that articulates with incus

Incus

middle of the three bones articulating with the stapes

Stapes

auditory ossicle that fits into the oval window on the cochlea

Bony labyrinth

spaces within the petrous portion of the temporal bone

Vestibular complex

detects balance and rotation containing the vestibule and semicircular canals

Cochlea

hearing organ

contains cochlear duct, scala vestibuli(superior), and scala tympani(inferior)

Maculae structure

contains hair cells that are sensory receptors for balance

Stereocilia

stiff microvilli on the apical surface of each hair cell

bending translates into electrical activity sent to brain via vestibular nerve

Kinocilium

one long cilium

bending translates into electrical activity sent to brain via vestibular nerve

Otolithic membrane

gelatinous mass that covers the surface of the stereocilia and kinocilia

Ampulla

an expanded region located within each semicircular canal

Crista ampullaris

an elevated region that contains the hair cells

Cupula

an overlying gelatinous dome where hair cells are embedded

Spiral organ

located within the cochlear duct and detects movement of endolymph

consists of thick sensory epithelium that includes hair cells and supporting cells on the basilar membrane

Tectorial membrane

an overlying mass that the stereocilia of hair cells project into

Endocrine glands

ductless organs that secrete hormones into the bloodstream

Hormones

can only affect target cells or target organs that have receptors for a specific hormone

Endocrinology

the study of the structural components of the endocrine system, the hormones they produce, and the effects of the hormones of target organs

Peptide hormones

growth hormone

Steroid hormone

estrogen and testosterone

Biogenic amines

thyroid hormone

Feedback loop

self-adjusting mechanism that regulates hormone secretion

Negative feedback loop

stimulus starts the process, a hormone is secreted in response to the elevated stimulus, and the hormone reduces the stimulus

example: eating a meal

Positive feedback loop

stimulus does not produce an opposite and counteracting effect, stimulus continues the process

example: breast feeding

Hypothalamus

the master gland of the endocrine system and is the interface between the nervous system and the endocrine system

Endocrine functions controlled by the hypothalamus

1. release of regulatory hormones that control the anterior pituitary

2. secretes antidiuretic hormone and oxytocin from the posterior pituitary

3. controls the stimulation and secretion activities of the adrenal medulla

Pituitary gland

located inferior to the hypothalamus and divided into anterior and posterior parts

Infundibulum

the thin stalk connecting the pituitary gland to the hypothalamus

Hypothalamo-hypophyseal portal system

blood vessel network that regulatory hormones travel through to the anterior pituitary

Hormones in the anterior pituitary

TSH, PRL, ACTH, GH, FSH, LH, MSH

Pituitary dwarfism

low growth hormone(GH) from birth