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Nervous System (SENSES :red_flag: (Types of Receptors based on stimulus…
Nervous System
SENSES
:red_flag:
Types of Receptors
based on
stimulus origin
:star:
Interoceptors
/ "visceroceptors"
Stimulus origin from internal organs
(e.g. digestive tube, bladder, lungs)
Monitor stimuli (changes in chemical concentration, taste stimuli, stretching of tissues, temperature).
Cause us to feel visceral pain, nausea, hunger, fullness.
Proprioceptors
Stimulus origin from muscles/ musculoskeletal organs
(e.g. skeletal muscles, tendons, joints, ligaments)
Monitor degree of stretch of these organs and send input on body movements to the CNS
Exteroceptors
Stimulus origin from environment
Located at or near body surface. Include receptors for touch, pressure, pain, and temperature in the skin & most receptors of the special sense organs.
Types of Receptors
based on stimulus type
:star:
Chemoreceptors
Respond to chemicals in solution (e.g. chemicals tasted or smelled) and to changes in blood chemistry.
Photoreceptors
In the eye. Respond to light.
Thermoreceptors
Respond to temperature changes
Nociceptors
Respond to harmful stimuli that result in pain.
Mechanoreceptors
Respond to mechanical forces (touch, pressure, stretch, vibrations)
Baroreceptor
A specific type of mechanoreceptor
Monitors BP
The eye components and visual pathways
:star:
The eye components
3 tunics of the eye
Vascular layer
Choroid
Nourishes the other layers. Deeply pigmented. Absorbs light and prevents scattering.
Continuous with
ciliary body
(a muscle that changes the shape of the eye).
Inner layer
Retina
Neural layer. Photoreceptors.
Optic Nerve
Fibrous layer
Sclera
White, dense CT, protective, anchor for muscle.
Cornea
Clear, transparent- Allows light into the eye. Involved with focusing light on retina.
Rods and Cones
Rods
MANY. Sensitive to light. Tells black and white and dim light.
Cones
FEWER. Allow us to see color. Best in bright light.
Lens and Iris
Both responsible for focusing light.
Lens
Posterior to iris. Focuses light on retina.
Iris
Anterior to lens. Intrinsic muscle. A sphincter muscle- dilates and contracts.
Other parts of the eye
Macula lutea
"Precise posterior pole"
Exactly opposite your pupil
Fovea centralis
At the center of maculalutea. Clearest vision here.
Optic disc
"Blind spot" No photoreceptors
Posterior and Anterior Cavities/Segments
Posterior segment
Largest segment/cavity- Everything posterior to lens and ciliary. Filled with vitreous humor. Supports retina and lens. Gel-like. Maintains normal pressure.
Anterior segment
Filled with aqueous humor which nourishes the lens and cornea. Also maintains normal intraocular pressure.
Anterior chamber
Between cornea and iris
Posterior chamber
Between iris and lens
Visual pathways
Path of light as it passes through the eye to the retina
CORNEA-PUPIL-LENS-POSTERIOR SEGMENT-RETINA
Path of nerve impulses from the retina through the optic nerve, optic chiasm, and optic tract to the brain
RETINA-OPTIC NERVE-OPTIC CHIASM-OPTIC TRACT-MIDBRAIN-THALAMUS-PRIMARY VISUAL CORTEX IN OCCIPITAL LOBE
Olfaction components and pathway
:star:
Components
Location
Roof of nasal cavity (superior nasal conche)
Structure
Pseudostratified columnar epithelium w/olfactory sensory neurons
Pathway
OLFACTORY RECEPTORS-OLFACTORY SENSORY NEURON W/IN THE OLFACTORY BULB-OLFACTORY TRACT- then to 2 places at once
Limbic system
Primary olfactory cortex in temporal bone
Gustation components and pathway
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Taste buds
Structure:
Epithelial cells
Location:
Tongue, inner cheeks, posterior wall of pharynx (throat), and epiglottis.
Cranial Nerves
3 that transmit taste information from tongue to brain.
Glossopharyngeal nerve- IX
Vagus nerve- X
Facial- VII
Path of nerve impulses from the gustatory receptors to the brain
3 FACIAL NERVES GO TO- MEDULLA OBLONGATA-THALAMUS-GUSTATORY CORTEX IN THE INSULA
Ear components and pathway
:star:
External/outer ear
Gather, funnel, and amplify sound waves
Auricle
Shell-shaped projection that surrounds the external acoustic meatus. Most is elastic cartilage covered with skin.
External acoustic meatus
Short tube from the auricle to the eardrum.
Middle ear
Tympanic membrane/ eardrum
Forms boundary between the external and middle ears
Auditory ossicles
Transmit vibrations
Inner ear
Cochlea
Pathway
COCHLEAR BRANCH OF CN VIII (the vestibulocochlear nerve)-- MEDULLA OBLONGATA-- PONS -- MIDBRAIN -- THALAMUS -- PRIMARY AUDITORY CORTEX IN TEMPORAL LOBE
Nervous System Organization
:red_flag:
PNS main structures and functions
Function
Be sensitive to stumuli and send information toward the CNS. Serve as communication lines that link all regions of body to CNS.
Structures
Spinal nerves- Carry signals to and from spinal cord.
Ganglia- Areas where the cell bodies of neurons are clustered.
Cranial nerves- Carry signals to and from brain.
Somatic division
Somatic sensory
The sensory innervation of the outer tube: Skin, body wall, and limbs.
General: Touch, pain, pressure, vibration, temperature, and proprioception from the skin, body wall and limbs.
Special: Hearing, equilibrium, vision.
Somatic motor
Stimulates contraction of skeletal muscles. "Voluntary nervous system."
CNS main structures and functions
Function
Receive, process incoming signals, and responds.
Structure
Brain and spinal cord
Autonomic division
Visceral Motor
Involuntary innervation of inner tube i.e. smooth muscle, cardiac muscle and glands; as well as some outer tube structures e.g. arrector pili muscle, smooth muscle in the vessels, and sweat glands.
Sympathetic divison
Parasympathetic division
Neurons
:red_flag:
3 Structural types of neurons
Bipolar
2 processes that extend on opposite sides from cell body: 1 is a fused dendrite, the other an axon. Very rare neurons occur in some special sensory organs (e.g. inner ear, olfactory epithelium of nose, retina of eye).
Unipolar/ pseudounipolar
Short. single process that emerges from cell body and divides/forms central and peripheral processes., which together comprise an axon.
Multipolar
Have more than 2 processes (usually numerous dendrites and one axon). 99% of neurons in body.
3 Functional types of neurons
Motor (efferent) neurons
Most are multipolar. Cell bodies will be in CNS usually and travel to muscle and glands (to contract and secrete).
Sensory (afferent) neurons
Majority are unipolar. Bipolar in special senses. Cell bodies located in ganglia of PNS.
Interneurons
or association neurons
Only in CNS between neurons. Multipolar. Most abundant of all neurons in body (99.98%)
Major components of a neuron
Chromatophilic substance (Nissl bodies)
Clusters of free ribosomes and rough ER.
Function= renew the plasma membrane and protein within the cytosol.
Axon hillock
Cone-shaped region of the cell body where axon arises from.
Nucleolus
Makes ribsosomes. All but smallest neurons have.
Neuron processes
Dendrites
Processes that branch from the cell body. Numerous. Function as receptive sites. Conduct electical signals toward cell body.
Axon
Only 1 per cell body. Impulse generators and conductors that transmit nerve impulses away from their cell body.
Nucleus
One nucleus per neuron
Cell body
Or "soma" Single nucleus surrounded by cytoplasm. All neurons have a cell body. Most neuron cell bodies located in CNS. Receptive region.
Axon collaterals
When an axon branches (only occasional) -- Extend from axon at more or less right angles.
Terminal arborization
When an axon branches profusely at its end.
Terminal boutons
(Axon terminals)
The very end knobs.
Anatomy of Nervous System
:red_flag:
Nerve components
Endoneurium
Loose CT
Fascicle
A bundle of axons
Myelin sheath
An insulating layer that covers some axons
Axon
Part of the neuron that carries a signal
Perineurium
Fibrous CT. Surrounds each fascicle.
Epineurium
Tough, fibrous CT. Surrounds nerve.
Nerve
Bundle of axon fascicles.
Glial cells
4 of CNS; 2 of PNS.
Ependymal cells
Simple cuboidal/simple columnar epithelium. Cilia keeps CSF moving. Lines spaces with cerebrospinal fluid called ventricles.
Satellite cells
in PNS. Found in ganglia. Surround neuron cell body. Structurally supportive. Regulates the exchange of materials in/out of neuron.
Oligodendrocytes
In CNS. Wrap their cell processes around the thicker axons producing the myelin sheath.
Microglial cells
In CNS. Phagocytes that wander and monitor. Remove microbes and damaged nerve tissue.
Astrocytes
In CNS. Most numerous glial cell. Many processes that contact neurons and capillaries. Supports neurons. Help maintain appropriate chemical environment.
Schwann cells
Make myelin sheath in PNS.