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Basic function of nervous system
sensory input (afferent), integration, motor output (efferent)
Parts of nervous system:
Central nervous system (CNS) and peripheral nervous system (PNS)
- CNS- brain and spinal cord
- PNS- Cranial nerves and spinal nerves, include ganglia
-outside of central body cavity senses. proprioception "sensing nes own body". special somatic senses: hearing, sight
-from the viscera, hunger nasea. Special visceral senses (chemical senses): taste and smell
- somatic (voluntary) motor-skeletal muscles
- visceral (involuntary motor- contraction and secretion of many glands, autonomic nervous sytem (involuntary nervous system)
Nervous tissue (two cell types)
neurons, neuroglia (support cells)
Neuron special characteristics
- can propogate an action potential
- extreme longevity
- they do not divide
- high metabolic rates
Cell body of neuron (soma=body)
- nissl (chromatophilic) bodies - clusters of rough ER
- neurofibrils- intermediate filaments that run between nissly bodies to resist tensile forces
- ganglia-clusters of cell bodies lie along nerves
- axon, initial segment, axon hillock, axonal transport (cytoskeleton), nerve fiber (can be a meter long), axon collaterals, terminal branches, axon terminals
- pre/post synaptic neuron, axodendritic/axosomatic synapses, synaptic vesicles, synaptic cleft, presynaptic/postsynaptic densities
Signals carried by neuron
Structural classification of neurons
number of processes that extend from the body
- multipolar neurons - 99% of neurons (lots of dendrites, one axon)
- bipolar neurons- two processes (one for dendrites one for axon) inner ear, olfactory epithelium of nose, retina of eye)
- unipolar neuron- "psuedounipolar" "T" process, typical sensory neuron
Functional classification of neurons
- Sensory neurons- pseudounipolar. central process is an axon, the peripheral process is also called an axon
- motor neurons-multipolar
- interneurons- only in CNS, 99.98% of neurons. multipolar, but vary in size and shape
Neuroglia in CNS
- much smaller and vastly outnumber neurons, can undergo mitosis
- Astrocytes- "star cells" with bulbous ends attached to neurons and capillaries. uptake glutamate from synapse, uptake/release ions
- microglia- elongated cell processes, macrophages of CNS
- ependymal cells- form simple epithelium, have cilia that circulate cerebrospinal flud
- oligodendrocytes-a few branches, wrap around axons and form myelin sheaths.
Neuroglia in PNS
- Satellite cells- surround neuron cell bodies
- Schwann cells- surround all axons and form myelin sheaths (myelin: a lipoprotein)
Myelin sheaths in PNS
- Schwann cells wrap around axons of rapidly conducting neurons with plasma membrane layers. External material is neuroilemma. nodes of ranvier.
- unmyelinated axons are on slow conducting neurons. Schwann cell can partly enclose 15 unmylenated neurons
Myelin sheath in CNS
Oligodendrocytes have multiple processes for different neurons. nodes are farther apart. Thinnest neurons are unmylinated and covered by glial cells
Grey and white matter of CNS
- grey matter- internal, has neuron cell bodies, dendrites, short unmylinated axons and neuroglia. (the cortex: superficial layer on cerebrum and cerebellum)
- white matter: superfical to grey matter. contains web of axons. white because of myelin sheaths.
- cablelike organ in the PNS with many axons (nerve fibers).
- covering each schwann cell is endoneurum, group of axons are bundled into fascicles by being wrapped in perineurium. The whole nerve is surrounded by epineurium
Integration between PNS and CNS
Afferent neuron send information to interneurons. Interneurons process, direct, initiate motor response in grey matter and transport information in white matter. Then send to efferent neurons
- account for reflexes, automatic motor responses.
- Can be as short as a single synapse (monosynaptic reflex), most are polynaptic (at least contain one interneuron)
neuronal circuits and patterns
information processes in series or in parallel (like when recognizing many features of a friend)
- large superior part of breain in charge of memory and reason.
- divided into hemispheres and 5 lobes.
- covers diencephalon and rostral brain stem like a mushroom
- has superficial gray matter of cortex, cerebral white matter and deep gray matter of the cerebrum
twisted ridge of brain
shallow grooves on the cerebral hemispheres
frontal lobe, parietal lobe, temporal lobe, insula lobe, occipital lobe
insula lobe is deep the the superficial surface of the brain
seperates the hemispheres of the brain which are connects through the corpus collosum
separates the frontal and temporal lobes, midwat connected to the central sulcus
- seperates the frontal and parietal lobes.
- anteriorly has precentral gyrus - primary motor cortex
- posteriorly has postcentral gyrus - somatosensory cortex
seperates the parietal and occipital lobes
corpus colosum (2 parts)
- lies superior to lateral ventricles. connects sides of the brain, parts of inner white matter
- genu- anterior portion
- splenium- posterior portion
- 80% of diencephalon, forms superiolateral walls of the third ventricle
- processes and relays information almost all the information that goes to the cerebral cortex
- interthalamic adhesion (intermediate mass)- connects left/right sides of the thalamus
- smooths body movements, controls coordination, and part of cognition,
- cerebellar hemispheres-each half of cerebellum
- vermis-connects hemispheres
- arbor vitae-"tree of life" composed of white matter, can be seen with sagittal cut
- Cerebellar puduncles- nerve fibers that connect cerebellum to brain stem
forms inferior wall of the third ventricle. Between the optic chiasma and posterior border of mamillary bodies, pituitary gland also projects inferiorly from hypothalamus
main visceral control center: autonomic nervous system
, emotional responses
(limbis system), body temperature
, hunger/thirst sensation
, motivational behavior
, sleep/wake regulation
, endocrine system
, memory formation
epithalamus: pineal gland
- most dorsal part of diencephalon.
- hormone secreting influenced by hypothalamus. secretes melatonin, which signal body for sleep.
- pineal gland is superior to the coropora quadrigemina
- two nodes inferior to the third ventricle, superior anterior to the pons.
- relay center for olfactory sensations
in the medial temporal lobe, under corticular surfacem part of limbic system, plays role in spatial navigation and long-term memory
small endocrine gland that project inferiorly from the hypothalmus, connected via the infundibulum
Grey matter of spinal cord
- central canal- contains CSF in the middle of the gray commisure.
- anterior horns- horns of the H of the matter
- posterior horns
- lateral horns- small lateral columns n the thoracic and superior lumbar region
Anterior median sulcus
posterior median sulcus
- three connective tissue membranes that protect the central nervous system
- Dura mater, arachnoid mater, and pia mater
- outermost most layer.
- Thick, leathery, made of dense connective tissue.
- Eternal to dura mater is epidural space (cushion of fat and veins)
- just deep to dura mater, superior to pia mater.
- weblike threads attach to pia mater
- innermost protective layer
- clings tightly to the spinal cord
- goes all the way to the coccyx and filum terminale, well below the spinal cord (ends between L1 and L2
Cerebral Spinal Fluid - CSF
- surrounds brain and spinal cords, protects from own weight and getting jostled.
- Similar to blood plasa except has more sodium and chloride ions and less protein
- made by choroid plexus, capillary rich membranes in the roof of 4 brain ventricles
Embryonic development of rostral part of neural tube
- Rostal part of neural tube becomes procencephalon (forebrain), mesencephalon (midbrain), and Rhombencephalon (hind brain).
- becomes Telecephalon and Diencephalon
- Telecephalon-Cerebrum (cerebral hemispheres, and lateral ventricles)
- Diencephalon-thalamus, hypothalamus, epithalamus and third ventricle
Embyonic Mesencephalon (midbrain) development
Mesencephalon stays as mesencephalon which becomes the midbrain and cerebral aqueduct
Embryonic rhombencephalon development
- rhombencephalon becomes metencephalon and myelencephalon
- below rhombencephalon is caudal portion of neural tube which becomes spinal cord
- metencephalon- Pons and cerebellum
- myelencephalon-medulla oblongata
4 parts of the brain
- brain stem- medulla oblongata, pons and midbrain
- diencephalon - thalamus, hypothalamus, epithalamus
Ventricles of the brain
- Lateral Ventricles, Third Ventricle, Central Aqueduct, Fourth Ventricle. (all attached together)
- Lateral ventricles- in cerebral heispheres, separated anteriorly by septum pellucidum, below corpus collosumThird Ventricle-in diencephalon, connects to laterals via interventricular foramen, between thalami
- Cerebral aqueduct- thin, tubelike
- Fourth ventricle- brain stem, forsal to pons and superiod half of medulla oblongata. Connects to central canal.
- choroid plexus- capillaries lining ventricles that produce CSF in fourth ventricle
The brain stem
Midbrain, pons and medulla oblongata
- -produces the automatic behaviors necessary for survival,
- -acts as passageway from cerebrum to spinal cord,
- -10 of 12 cranial nerves attach to it.
- Conical, lowest part of brain stem, connects to spinal cord at foramen magnum.
- regulates: breathing, heartbeat and blood pressure
- between medulla oblongata and midbrain
- contains respiratory centers.
- the cerebellar peduncles link the cerebellum with the pons, this is wherecerebellum received motor movement information
- the most superior part of the brain stem lying between the diencephalon (thalami) and the pons.
- cerebral peduncles- ventral part of the midbrain form vertical pillars
- corpora quadrigemia-make up the tectum, the anterior part of the midbrain. has four colliculi ("little hills") on the dorsal part
- superior collicus-visual reflexes (turning our head when we see something in the periphery)
- inferior collicus-reflexive responses to sounds
Blood brain- barrier
- special endothelium of brain capillaries that is sealed with tight junctions.
- Fat and gas can pass through and other molecules through active transport
originating from subclavian artery, pass through the foramen magnum to unite and form basilar artery
central artery anterior to brain stem that branches to cerebellum, pons and inner ear
internal carotid arteries
paired, from common carotid arteries, passing through carotid canal of temporal one
cerebral arterial circle of Willis
- encircles the pituitary gland uniting anterior and posterior circulations
Cranial nerves: Where do they attach? What do they innervate? What is the mnemonic?
- 12 cranial nerves.
- first two attach to the forebrain, the others to the brain stem.
- They all innervate the head and neck except vagus nerve (X) which extends to abdomen.
- Oh Oh Oh, To Touch And Feel Very Good Velvet, AH.
Cranial Nerve I
- Olfactory: Smelling nerves
- purely sensory, Has olfactory bulb and olfactory tract (passes through to cerebral cortex of occipital lobe to be interpreted
Cranial Nerve II
- Optic nerve: arises from retina of the eye
- Creates X on forebrain. Optic Chiasm is center of the X, Optic tract is posterior to chiasm leading to the thalamus
- Purely sensory
Cranial Nerve III:
- Oculomotor: "eye mover"
- innervates four four muscles that move the eye around, constricts pupil
Cranial Nerve IV
- Trochlear Nerve: "pulley", motor nerve
- arises near corpora quadrigemina of inferior colliculi
- enters the superior orbital fissure to innervate superior oblique muscle of the eye that
Cranial nerve V
- largest cranial nerve, originates lateral to pons
- Sensory:face, teeth and tongue, Motor: mastication muscles
- Good for dentists to numb
- Opthalamic division I: transmitted through superior orbital fissure, innervates forehead and scalp
- Maxillary division V2: through foramen rotundum to upper jaw region
- Mandibular division V3: through foramen ovale, lower jaw region
Cranial Nerve VI
- Abducens: "abducts" the eye
- innervates the lateral rectus of the eye through superior orbital fissue
Cranial nerve VII
- Facial Nerve:
- just lateral to pons, first of four nerves in a row.
- Through stylomastoid foramen, internal acoustic meatus, innervates facial expression, salivary glands, taste buds (sensory) and lacrimal gland (tears)
Cranial Nerve VIII
- Vestibulocochlear nerve
- enters at pons and medulla border, inferior to facial nerve VII, through internal acoutic meatus
- involved in equilibrium and balance. Sensory: hearing, balance and posture
Cranial Nerve IX
- Glossopharyngeal nerve
- From medulla, leave through jugular foramen. Innervates swallowing and salivary gland muscles (motor) and taste buds (sensory)
Cranial nerve X
- Vagus nerve:
- through jugular foramen, innervates muscles for swallowing, respitory tract, heart, esophagus, and abdominal viscera. 70% of parasmpathetic division of ANS
Cranial nerve XI
- Accessory nerve:
- On medula and spinal cord. through jugular foramen.
- innervates trapezius and sternoclaidomastoid to move head, neck and shoulders (strictly motor)
Cranial nerve XII
- Hypoglossal nerve
- more in front of medula.
- Goes through hypoglossal canal to innervate the tongue muscles (motor)
- 31: 8-cervical, 12-thoracic, 5-Lumbar, 5-Sacral, 1-Coccygeal
- Each spinal nerve connects to spinal cord via dorsal (sensory) and ventral (motor) roots.
- Lateral to spinal nerves, they branch into dorsal (dorsal truck and neck) and ventral (limbs, anterior neck and truck) rami
Brachial plexus: The ventral rami, trunks and divisions and cords
- intermixing of ventral rami C5-C8 and T1. Supplies nerves for upper limb
- The rami combine to form upper, middle and lower trunks.
- These in turn divide to anterior and posterior divisions.
Brachial plexus: From Divisions to cords to terminal branches
mnemonic for sequence
- All anterior and posterior divisions become lateral, medial and posterior cords.
- posterior divisons all become posterior cord
- upper and middle anterior become lateral
- lower anterior becomes medial
offee = Roots, trunks, divisions, cords
- terminal of lateral cord
- passes through and innervates coracobrachialis, goes between biceps brachii and brachialis. ennervates skin on anterolateral forearm
- of the brachialis plexus
- from lateral and medial cords
- innervates muscles of the forearm and (lateral 2/3 of skin) and muscles of the hand
- brachialis plexus, braches off of medial cord
- follows ulna to supply the flexorcarpi ulnaris, and ulnar part of flexor digitorum profundus
- brachial plexus, originates from posterior cord
- deep to the other nerves
- innervates posterior upper arm (triceps and skin). innervates skin of posteriolateral surface of forearm,and extensor muscles
- innervates lower limb
- Lumbar plexus originates from L1-L4, and goes through psoas major. Largest terminal is the femoral nerve
- Sacral plexus originates from L4-S4. largest branch is the Sciatic nerve
- largest nerve from the lumbar plexus. Runs down anterior thigh
- largest nerve in the body. From the sacral plexus and emerges just below the piriformis muscle and runs down posterior thigh.
- on lower upper leg splits into:
- Tibial nerve: medial branch runs along back of leg until branching in the heal
- common fibular (peroneal) nerve: lateral and smaller branch, branches at top third of lower lateral leg
- Composed of skeletal muslces attached to the hyoid bone
- contains most of the taste buds. Attached to the floor of the oral cavity via lingual frenulum.
- Has rough surface called papillae.
- filiform papillae-smallest and found on anterior 2/3 of tongue
- Fungiform papillae- intermediate size scattered on the tip and sides of tongue
- circumvallate-the largest of the papillae on the back of the tongue in a V shape
intermingled with taste buds which sends taste information through gustatory pathway of: The facial nerve VII, glossopharyngeal nerve IX.
- olfactory epithelium is psuedostratified columnar epithelium. There are many type of olfactory receptor cells that are surrounded by columnar supporting cells.
- receptor cells have cilia that project onto epithelial surface (mucus dissolved odors). the receptor cells join into filaments of olfactory nerve which penetrate the cribiform plates.
- Mitral cells relay message from olfactory bumb to the rest of the brain