nervous and sensory systems

nerve tissue

neurons: structural units of nervous systems

neuroglia support the functions of neurons

Each neuron consists of a cell body, soma, with extensions called an axon and one or more (sometimes many) extensions called dendrites.

Dendrites receive electrical nerve impulses and conduct them toward the cell body and the axon.

Axons conduct nerve impulses away from the cell body. Most neurons have a single axon arising from the axonal hillock on the cell body.

Neuroglia comprise almost half the brain and spinal cord tissue and are much more numerous than neurons. They support, nourish, and protect neurons.

CNS

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synapses, neurons communicate

chemical synapses :release and receive chemical neurotransmitters.

electrical synapses: Electrically coupled neurons allow for rapid transmission across electrical synapses.

neurotransmitters: effects on sleeping, anger, thinking.

divisions of the nervous system

central nervous system

peripheral nervous system

consists of the brain and spinal cord, located in the dorsal body cavity.

receives information from and sends information to the body.

key decision maker

consists of 12 cranial nerves and 31 spinal nerves

messenger

The brain and spinal cord are connected via the brain stem,

Cerebrum: largest part, controls higher brain functions

Basal nuclei: masses of gray matter, rleays motor impulses from cerebral cortex.

Diencephalon: masses of gray matter, thalamus: relays sensory impulses ascending from other areas of nervous ststem

cerebellum: large tissue, communicates with rest of CNS

The brain

cerebrum: largest part, controls higher brain functions

basal nuclei: masses of gray matter that relays motor impulses from cerebral cortex, passing into brain stem and spinal cord.

Diencephaloon: masses of gray matter that relays sensory impulses ascending from other areas of nervous system

brain stem: midbrain, poris and medulla oblongata. Refkex centers move eyes, head, maintain posture.

cerebullum: large tissue mass, communicate with rest of cns via tracts.

PNS

peirpheral nerves connecting cns to other parts of body

sensory

motor

somatic nervous system oversees conscious activities

sensory receptors of the PNS are specialized to respond to stimuli.

general senses of touch, pressure, temperature, and pain are spread throughout the body via muscle, joint, skin, and visceral receptors.

eflex is actually defined as a fast, automatic response to a specific stimulus. Reflex activity in the human body can be either inborn (innate) or learned (acquired).

Impulses are carried toward the CNS from the body’s sensory receptors.

Impulses are carried from the CNS to the effector organs, activating muscles to contract and glands to secrete.

Somatic motor fibers transmit impulses from the CNS to the skeletal muscles.

autonomic nervous system oversees unconscious activities

The ANS contains visceral motor nerve fibers regulating glandular, cardiac muscle, and smooth muscle activity

preganglionic neurons are the cell bodies of the first neurons and are found in the brain or spinal cord.

arasympathetic division functions in an opposite manner and is part of the rest-and-digest response.

sympathetic division prepares the body for stressful or emergency situations and is part of the fight-or-flight response.

Dual innervation of the autonomic nervous system helps to balance the sympathetic and parasympathetic divisions

effects of ageing on nervous system

risk of stroke

atty deposits accumulate in the blood vessels, there is a decrease in blood flow to the brain.

increase the chances that an affected vessel will rupture,\

slower reaction time

loss of neurons

brain processes nerve impulses more slowly, performance of certain tasks and reaction times often become slower

Neuronal loss and shrinkage causes a decrease in brain weight and size.

increase in neuroglia and deposits

Brain neurons accumulate abnormal intracellular deposits. Extracellular plaques may affect memory processing. When deposits and plaques exceed normal amounts caused by aging, clinical abnormalities may occur.

characterteristics of alzheirmers

change in transmission efficiency

Decreased numbers of functional nerve cells may reduce the strength of the message being transmitted.

Anatomy and function of sensory system

central nervous system (CNS) processes and interprets nerve impulses from sensory receptors that detect environmental changes.

olfaction-sense of smell

works with sense of taste

masses of epithelium covering the upperpart of the nasal cavity, superior nasal conchae, and part of the nasal septum.

Olfactory receptor cells have hair-like cilia, which help to differentiate among odors.

Odorant molecules must partially condensate from gases to fluids before receptors can detect them.

Gustatory-sense of taste

Taste pores have tiny projections called taste hairs, which are the sensitive parts of the taste receptor cells.

auditory-sense of hearing

detection of sound and the detection of body position,

The ear consists of three separate portions: the external (outer), middle, and inner parts.

external ear:

Auricle (pinna): A funnel-shaped structure composed of elastic cartilage, thin skin, and small amounts of hair

External acoustic meatus. Glands secrete cerumen, a yellow-brown waxy substance

trap foreign particles and repel insects from entering the ear.

The auricle functions to funnel sound waves to the external acoustic meatus.

Eardrum (tympanic membrane):

A semitransparent membrane covered by thin skin on the outside and mucous membrane on the inside that moves back and forth in response to sound waves

middle ear

middle ear (tympanic cavity) inside the petrous portion of the temporal bone is filled with air and contains the auditory ossicles (the malleus, incus, and stapes). These bones are attached to the tympanic cavity wall by ligaments and bridge the eardrum and inner ear to transmit vibration

inner ear

cochlea, which functions in hearing.

The vestibule and its two expanded chambers (the utricle and saccule),with a tiny macula containing many sensory hair cells function in equilibrium.

visual-sense of sight

(1) eyebrows, (2) eyelids, (3) eyelashes, (4) conjunctiva, (5) lacrimal apparatus, and (6) extrinsic eye muscles.

eyebrows consists of coarse, short hair that shade eyes from light and trap perspiration

eyelid has skin, muuscle, connective tissue and conjunctiva that protext anterior portion of the eye

conjuctiva is a thin transparent mucuos membrane associated with eyelids

eye is hollow, spherical and about 2.5cm in diameter

extrinsic eye muscles: ability to move the eye

refraction: as light waves enter eye, image of the object is focused on the retina

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neuronal pathways for vision:Ganglion cell axons extend to the lateral geniculate ganglion of the thalamus, where they synapse. From there, neurons form the optic radiations that project to the visual cortex.

Sensory: Conduct action potentials toward the CNS.

motor: conduct action potentials away from the CNS toward muscles or glands

interneuron: conduct action potentials within CNS from one neuron to another, between sensory and motor neurons