Nervous System
PATRICK L, LUCAS B, TANNER A, JAVIER C.
Basic Functions
Sensory Function
◦ This part of the nervous system is conducted by sensory receptors at the end of peripheral
neurons
◦ Sensory receptors detect change both inside and outside of the body
◦ They monitor light, temperature, sound and any other environment factors
Integrative Function
◦ After the sensory receptors send the information to the central nervous system, the impulses
are integrated, or grouped together to form sensations
Basic Functions (Cont.)
Motor Function
◦ Reacting to impulses
◦ Peripheral neurons carry impulses away from the central nervous system to
responding structures called effectors (muscles, glands)
◦ Can be split into two categories
◦ Somatic: controlled, voluntary
◦ Autonomic: involuntary
Neurons
•The neuron is made of two main parts, the cell body and the
axon
•The cell body houses the nucleus and chromatophilic substance
•Dendrites extend from the cell body and brings information into
the neuron
•The axon also extends from the cell body, but instead takes the
information away from the cell body
•The axon is surrounded by a protective layer known as the myelin
sheath which is created by Schwann cells surrounding the axon
•Nodes of Ranvier allow impulses to reach the axon’s end as it
would be nearly impossible if the axon was completely wrapped
in the sheath
The Synapse
A Synapse is a junction between two communicating neurons.
Synaptic Transmission
• Gap in between neurons is the synaptic cleft.
• The presynaptic neuron carries impulse to the synapse, and the postsynaptic neuron is the
receiver.
• Process of crossing synaptic cleft is called synaptic transmission. (ST)
• Neurotransmitters are biochemically responsible for the one way process of ST.
• Distal end of axons contain synaptic knobs.
• Synaptic knobs contain synaptic vesicles that release neurotransmitters.
Excitatory and Inhibitory Actions
Excitatory
Inhibitory
•Neurotransmitters that increase postsynaptic
membrane permeability are excitatory.
•Neurotransmitters that increase postsynaptic
membrane permeability are excitatory.
•If most neurotransmitter s released are
excitatory, then it will reach threshold.
•If most neurotransmitter s released are
excitatory, then it will reach threshold.
•Neurotransmitters: Acetylcholine,
norepinephrine
•Neurotransmitters: Acetylcholine,
norepinephrine
Neurotransmitters
• Neurotransmitters are synthesized in the cytoplasm of the synaptic knob and stored in
synaptic vesicles.
• When action potential reaches membrane of synaptic knob, permeability to calcium ions
increases.
• Synaptic vesicles fuse with membrane and release into synaptic cleft.
• The vesicle breaks away from membrane and return to cytoplasm to retrieve more
neurotransmitters.
• Decomposed in synaptic cleft by enzymes.
• Some are transported back to synaptic knob that released them or into nearby neuroglial cells.
Central Nervous System (CNS)
Comprised of the Spine and Brain
◦ Sensory receptors convert into nerve pulses and sent here
◦ Signals integrated creating sensations, adding to memory, producing thoughts
Integrative functions
◦ Conscious/subconscious thoughts and decisions
◦ Functions employ peripheral neurons – carry impulses from CNS to effectors
◦ Muscles, glands associated with movement
Peripheral
Nerves that branch from CNS to rest of body
Divided into somatic and Autonomic systems
◦ Somatic oversees conscious movement
Consists of 12 Cranial Nerves – all but 1st pair originating from brainstem
◦ Pass through foramina and lead to head neck and trunk
◦ Name and number designate cranial nerves
◦ Numbers: Front to back
◦ Names: primary function
Cranial Nerves
Olfactory (I)- sense of smell
◦ Upper nasal cavity
◦ Senses carried to olfactory in bulbs then cerebral centers
Optic (II)- Vision
◦ Eyes to brain
◦ In ganglian cell layers in eyes (mass of nervous tissue)
◦ Axons pass through optic foramina to pathways of brain and interpreted
in visual cortices of occipital lobes
Oculomotor (III)- Adjust lighting (pupils)
◦ Each component of nerve connect to voluntary part of eyelid (4 of 6)
Cranial Nerves
Trochlear (IV)- Lighting
◦ Arise from midbrain
◦ Carries motor impulses to 5th voluntary muscle-moves eye
Trigeminal (V) Eyes, Upper, lower mouth
◦ Mixed nerve
◦ 3 sensory components- Ophthalmic, maxillary, Mandibular
◦ Opth.-Send impulses to eye, tear glands, anterior scalp, forehead, upper
eyelid
◦ Max.- to upper teeth, gum, lip, skin of face, mucous lining of palate
◦ Man- Motor: muscles of mastication, some in floor of mouth. Sensory:
scalp behind ear, jaw, lower teeth, jaw, lip
Cranial Nerves
Abducens (VI)- remaining impulses to eye
Facial (VII)- some fibers transmit for facial expressions
◦ From lower parts on pons
◦ Anterior 2/3 of tongue
Vestibulocochlear (VIII)- 2 Parts
◦ Vestibular: located on ganglia of inner ear
◦ Maintains equilibrium
◦ Cochlear: located inner
◦ Interprets sounds
Glossopharyngeal (IX)- pharynx and tongue
◦ Sensory: Signals to pharynx and tonsils, posterior 1/3 of tongue
◦ Motor: innervate muscles of pharynx- swallowing
Cranial Nerves
Vagus (X)- Neck, chest, abs
◦ Somatic: impulses to larynx- speech, swallowing
◦ Autonomic (Predominant): heart, smooth muscles, glands in thorax and
abdomen
Accessory (XI)- both cranial and spinal
◦ Cranial: joins vagus nerves
◦ Spinal: supplies motor fibers of trapezius/ sternocleidomastoid
Hypoglossal (XII)- tongue
◦ From medulla to tongue
◦ Helps in speaking chewing swallowing
Spinal Nerves
There are 31 pairs
◦ Mixed nerves
◦ Provide two-way communication
between spinal cord and upper and lower limbs
◦ Also neck and trunk
◦ Not individually named- Grouped according to level
◦ 8 cervical pairs
◦ 12 Thoracic pairs
◦ 5 Lumbar pairs
◦ 1 Coccygeal pair
Spinal Nerves
Emerges from cord by two dorsal roots
◦ This forms with a ventral root to form a nerve
Except in thoracic region, main portions of nerve form to make plexuses
◦ Cervical plexuses lie deep in neck (C 1-4)
◦ Supply muscles of skin of neck
◦ C 3-5 pass into phrenic nerves-impulses to diaphragm
◦ Brachial plexuses (C5-T1_
◦ Deep in shoulders
◦ Supply muscles and skin of arm, forearm, hand
◦ Include musculocutaneous, ulnar, median, radial, and axillary nerves
Spinal Nerves
Lumbosacral Plexuses (T12-S5)
◦ Give rise to motor and sensory fibers in lower abdominal wall, external
genitalia, buttocks, thighs, legs, and feet
◦ Major branches are obturator, femoral, and sciatic nerves
T2-T11
◦ Do not enter plexuses
◦ Become intercostal nerves- give impulses to intercostal muscles and upper abdominal wall
◦ Also receive sensory impulses from skin of thorax and abdomen
Autonomic Nervous System (ANS)
Part of PNS- functions independently
Controls visceral functions by regulating smooth muscles, cardiac glands
◦ Heart rate, blood pressure, breathing rate, body temperature (Homeostasis)
Two sublevels
◦ Sympathetic Division- Fight or Flight
◦ Parasympathetic Division- Normal Conditions
Sympathetic
Preganglionic Fibers originate from neurons in gray matter of spine
◦ Axons leave through ventral roots of spinal cord in T1-L2
◦ Enter a member of a chain of paravertebral ganglia
◦ Forms synapse with 2nd neuron
◦ Post ganglionic fiber returns to a spinal nerve
Parasympathetic
Fibers arise from brainstem and sacral region of spine
Lead in outward in cranial or sacral nerves to ganglia
Postganglionic fibers continue from ganglia to specific muscles or glands within viscera
Autonomic Neurotransmitters
◦ Control if effect will be sympathetic or para.
◦ Both secrete acetylcholine- sympathetic secrete norepinephrine- adrenergic fibers
Somatic Nervous System
•Controls Skeletal Muscles
•Also controls external sensory organs (Skin)
•This system is said to be voluntary because the
responses can be controlled consciously.
•Enables humans to react consciously to
environmental changes
Somatic Senses
Touch and Pressure
• Light touches are detected by Meissner's
corpuscles
• Deep pressure is detected by Pacinian
corpuscles.
Somatic Senses
Sensation of Temperature
• Free Nerve Endings detect temperature.
Sensation of Pain
• Pain can be sensed through the skin, like temperature, touch and
pressure
• Can also be sense in our Viscera’s
Somatic Senses
Sensation of Muscles
◦ Muscle senses tell us about the position of our bodies in space and how much force
we are currently using in any muscle
◦ Uses Muscle Spindles in order to sense
Relationship: Taste and Smell
•Ever wonder why food taste different when you have a cold?
•Without the other, your senses can be impaired.
•Taste buds vs. Odorants