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