Exam 4 Flashcards
Chapter 12 vocab
Neuron-nerve cell that generates & transmits electrical signals
- *Nerve fiber**- a long axon
- *Nerve**- a bundle of nerve fibers (axons) in the PNS
- *Tract**- bundle of nerve fibers (axons) in the CNS
- *Ganglion**-cluster of neuron cell bodies
- *Synapse** (terminate)- junction between two communicating cells
- *Effector cells**- activated by a motor signal (muscles contract, glands secrete)
- *Electrochemical communication**- the means of communication between nerve cells (signals & neurotransmitters)
- *Action potential-** change in ion concentration across the membrane, and runs down the axon
- *Graded potentials**- local depolarization, havent reached the threashold, not all or nothing like action potential.
receptor- PNS cell that senses stimuli(sensory)
- *Afferent**- sensory input
- *Efferent**-Motor output
ANS (autonomic nervous system)
Visceral motor (smooth muscle, cardiac muscle, glands)
Properties of Neurons
- *Excitability**- respond to stimuli
- *Conductivity**-use electrical signals
- *Secretion**-release of a chemical
- *Electrochemical**-response to stimuli!
Functional Classes of Neurons
- *Sensory (afferent)**- almost always end in the brain and spinal cord
- *Interneurons**- always in CNS. located between sensory & motor (thus “inter”) Integrative- process, store, retrieve, make decisions. 90% of all neurons.
- *Motor (efferent)**- end (terminate) on effector cells- cells that can do a job- skeletal muscle, smooth muscle, cardiac muscle, or glands.
Structural Classes of Neurons
Multipolar-
Most common in CNS
Two or more dendrites
All motor neurons
Interneurons- Multipolar
Bipolar-
One axon; one dendrite
Olfactory cells; retina; ear
sensory
Unipolar- single process from soma; “pseudounipolar”;
Peripheral
Central process
exclusively sensory
Glia Cells: supportive cells of CNS
CNS
Astrocytes: most abundant, help with glutamate(neurotransmitter) re-uptake from synapses and ion control.
Microglia: least abundant and engulf invading microorganisms and dead neurons
Ependymal cells- aid in circulation of cerebrospinal fluid (CSF) and line CSF cavities in the brain and spine.
Oligodendrocytes: myelin sheaths (similar to Shwan cells of the PNS)
Supportive cells of the PNS
Satellite cells: surround cell bodies in ganglia
Schwann cells: form myelin sheaths
Nerve regeneration
NO CNS regeneration!
very limited, only possibility is if the axon is what is damaged, no repair of cell body.
Macrophages come in and eat damaged parts. Shwan cells try to fix.
Brain matter
- *White matter**- (message relay) constitutes mylenated axons.
- *Grey matter**- Everything else, where all the processing/intergration takes place, and intiating motor response signals.
Structure of a Nerve
Within a nerve, each axon is surrounded by Schwann cells. Covering the Schwann cells is loose connective tissue called endoneurium. Groups of axons are called nerve fascicles and wrapped in perineurium, the whole nerve is wrapped in tough connective tissue called the epinerium.
Reflex Arch
Reflex arcs are simple chains of neurons that cause our simplest, reflexive behaviors and reflect the basic structural plan of the nervous system.
reflex- rapid, automatic motor responses to
stimuli.
monosynaptic reflex- there is no interneuron between the sensory neuron and the motor neuron; thus, as its name implies, there is only one synapse in this reflex arc. The example shown is the familiar “knee-jerk” reflex.(stretch reflexes)
polysynaptic reflexes (most common) in which
one or more interneurons are part of the reflex pathway
between the sensory and motor neurons. (Withdrawal reflexes)
basic design of the spinal cord and the brain
gray matter is a gray-colored zone that surrounds the hollow central cavity of the CNS. In the spinal cord it is a butterflyshaped region in which the dorsal half contains cell bodies of interneurons and the ventral half contains cell bodies of motor neurons. Thus, gray matter is the site where neuron cell bodies are clustered. More specifically, the gray matter of the CNS is a mixture of neuron cell bodies; dendrites; short, unmyelinated neurons; and neuroglia.
white matter, which contains
no neuron cell bodies but millions of axons. Its white
color comes from the myelin sheaths around many of the axons. Most of these axons either ascend from the spinal cord to the brain or descend from the brain to the spinal cord, allowing these two regions of the CNS to communicate with each other. Thus, white matter consists of axons running between different parts of the CNS. Within the white matter, axons traveling to similar destinations form axon bundles called tracts.
Embryonic Development of the Brain
Neural Tube: Anterior: rostral; Posterior: caudal
primary brain vesicles:
- *prosencephalon (forebrain)**→Adult: Cerebrum, thalamus (hypothalamus,
epithalamus) , and retina - *mesencephalon (midbrain)**→ Adult: Brain stem: midbrain
- *rhombencephalon (hindbrain)**→ Adult: Brain stem: pons, Cerebellum Brain stem: medulla oblongata
Cerebrum & Cerebral Cortex
- *Cerebrum** (85% of brain mass)
- *Cortex** (gray matter)
- *White matter**
- *Hemispheres** (left & right)
- *Corpus Callosum** (join hemispheres)
- *Convolutions**- gyri (raised) and sulci (depression)
- *Longitudinal Fissure** (deep sulcus)
Cerebral Cortex:
Divided into lobes by distinctive sulci
Contains cell bodies, dendrites and short unmyelinated fibers
Only 2-4mm thick
Divided into structural and functional (distinct sensory and motor) regions
Motor- controls voluntary motor functions
Sensory- conscious awareness/interpretation of incoming sensation
Association areas- integrate diverse information into purposeful action
Lobes:
Frontal
Parietal
Temporal
Occipital
Insula
Cerebrum
Frontal Lobe
Frontal Lobe (everything anterior to the central sulcus)
Primary motor cortex (Precentral gyrus)-initiates voluntary skeletal movement
Broca’s motor speech area (left hemisphere is speech production; right hemisphere controls emotional overtones)
(Also premotor cortex –planning- and frontal eye field)
Task management, multitasking, reading
Cerebrum
Sensory Cortex
(Everything posterior from the central sulcus)
distinct areas for conscious awareness of somatic senses (taste, vision, touch, smell, hearing)
Temporal lobe
Parietal lobe
Occipital lobe
insula
Cerebrum
Parietal Lobe
Association area (ex. that noise is an alarm, not the doorbell)
- *Sensory map**: stimulate cells to produce sensations in these areas
- *Contralateral**
- *Primary Somatosensory Cortex**- conscious awareness of senses
- *Gustatory Cortex** (overlaps w/ insula)-conscious awareness of taste
Cerebrum
Temporal Lobe and Insula
Temporal lobe
- *Primary Auditory Cortex**- conscious awareness of sound
- *Auditory Association Cortex**- Wernicke’s area (left side understand spoken word; right side emotional overtones)
**Insula**- deep within lateral sulcus Vestibular Cortex (balance/equilibrium)
Cerebrum
Occipital Lobe
Primary Visual Cortex- what you’re seeing, and in context.
Calcarine sulcus-landmark where you find the visual cortex
Damage to this lobe–> blindness
Cerebrum
Basal Nuclei
Clusters of grey matter deep within white.
Basil Nuclei (ex. Corpus Striatum)- cooperate with cerebral cortex in controlling movements. How hard, how fast, which muscles to activate.
Also, plays a role in recieving stimuli and delivering it to the motor part of the brain.
Diencephalon
(purple)
Diencephalon:
(thalamus, hypothalamus,
epithalamus), retina
Thalamus: the sensory routing area surrounds 3rd ventricle (canal). Any sensory has to pass through the Thalamus.
- *Hypothalamus**(inferior to Thalamus):
- Hormone Secretion (controls anterior pituitary) and hormones that are stored in posterior pituitary
- Autonomic effects
- Thermoregulation (shiver vs sweat)
- Food and water intake
- Sleep and circadian rhythms
- Emotional responses
- Memory
- *Epithalamus**- has/is mostly pineal gland and most dorsal part of thalamus.
- *Penial gland**: produces & secretes a hormone called melatonin which regulates sleep cycles, aids in sleep.
Brainstem: Midbrain (mesencephalon)
Cranial Nerve (3,4)
- *Tectum- Corpora Quadrigemina:**
- *Superior colliculi** (vision and visual reflexes)
- *Inferior colliculi** (hearing and auditory reflexes)
- *Substantia Nigra** (works with basal nuclei); inhibitory signals to thalamus and basal nuclei.
- Controls unwanted muscle movement
- Parkinson’s Disease and resting tremors (sign of degeneration of Sub N)
Cerebral Aqueduct
Pons- Metencephalon
4th ventricle between pons and cerebellum
Cranial Nerve (5-8)
respiration, and bladder control inputs
Hearing, facial sensations, taste, saliva, tears, facial expression, equilibrium, eye movement (lateral rectus)
Medulla Oblongata- (Myelencephalon)
(dark green)
Continuous with spinal cord at foramen magnum
Cranial Nerves (9-12)
Pyramids- long axons that leave the frontal motor cortex and terminate at the medulla causing ridges on ventral side of medulla
Points of decussation (axons cross over to opposite side of body)
Regulates blood pressure (vasomotor center), heart beat/rate (cardiac center), and breathing (respiratory center)
Part of 4th ventricle found here
Nerve vs tract
Nerve: collection of axons within the PNS.
Tract: collection of axons within the CNS
Cerebellum
Cerebellum- Not part of brain stem but still metencephalon
- Smoothes and coordinates body movements
- Helps with posture and equilibrium
- Receives input from eye, ear, and spinal cord
- *Folia**- like foliage (grey)
- *Arbor vitae**-tree trunk (white)
Choroid Plexuses
Choroid plexuses- sites of CSF synthesis (red)
Subarachnoid space- blue
The Spinal Column
Spinal nerves exit thru intervertebral foramina as: 8C,12T,5L,5S,1C
31 pairs of nerves
Conus medullaris-spine starts to taper (get thin)
Cauda equina- “horse tail”
Cervical and Lumbar enlargements
Ventral median fissure
Dorsal median sulcus
Gross Anatomy of Spinal Cord
Gray matter
-horns
Gray commissure-grey little bridge
Central canal-hole in center
Primary rami
Meninges-dura matter, arachnoid,pia
Dorsal root ganglion
Roots
White matter
Decussation/contralateral-crossing over (think optical tract)
ipsilateral
**Spinal Nerves
31 pairs—contain thousands of nerve fibers
Connect to the spinal cord
Named for point of issue from the spinal cord
8 pairs of cervical nerves (C1–C8)
12 pairs of thoracic nerves (T1–T12)
5 pairs of lumbar nerves (L1–L5)
5 pairs of sacral nerves (S1–S5)
1 pair of coccygeal nerves (Co1)
They carry both sensory and motor fibers
- Connect to the spinal cord by the dorsal root and ventral root
- *Dorsal root**—contains sensory fibers
- *Cell bodies**—located in the dorsal root ganglion
- *Ventral root**—contains motor fibers arising from anterior gray column
Branch into dorsal ramus and ventral ramus
Dorsal and ventral rami contain both sensory and motor fibers
Rami communicantes connect to the base of the ventral ramus
Lead to the sympathetic chain ganglia
***Location of Cell Bodies
Sensory- dorsal root ganglion
- *Somatic motor**- ventral horn of spinal cord
- *Visceral motor**-lateral horn of the spinal cord
interneurons(CNS) -cell bodies start and end in spinal cord’s Dorsal horn
Brachial Plexus
Brachial plexus lies in the neck and axilla
Formed by ventral rami of C5–T1
Give rise to main nerves of the upper limb
- *Musculocutaneous**—main branch of the lateral cord
- Innervates the biceps brachii and brachialis
- *Median**—originates from both lateral and medial cords
- Innervates anterior forearm muscles and lateral palm
Ulnar—branches from the medial cord
Innervates intrinsic hand muscles and skin of the medial hand
Radial—continuation of the posterior cord
Largest branch of the brachial plexus
-Innervates muscles of the posterior upper limb
Axillary
-Innervates the deltoid and teres minor
Damage to Brachial Plexus:
Wrist Drop (Waiter’s Hand)(C) Claw Hand(B) Crutch paralysis (axillary nerve) Hand of Benediction (A)-can’t flex
The Lumbar Plexus
Lumbar plexus
Arises from L1– L4
Smaller branches innervate the posterior abdominal wall and psoas muscle
Main branches innervate the anterior thigh
Femoral nerve—innervates anterior thigh muscles
Obturator nerve—innervates adductor muscles
The Sacral Plexus
Arises from spinal nerves L4–S4
Caudal to the lumbar plexus
Often considered with the lumbar plexus
Sciatic nerve—the largest nerve of the sacral plexus
Actually two nerves in one sheath
Tibial nerve—innervates most of the posterior lower limb
Common fibular (peroneal) nerve—innervates muscles of the anterolateral leg
Innervation of the Skin: Dermatomes
Dermatome—an area of skin
-Innervated by cutaneous branches of a single spinal nerve
Upper limb
-Skin is supplied by nerves of the brachial plexus
Lower limb
-Lumbar nerves—anterior surface
-Sacral nerves—posterior surface
Reflexes
- Involuntary
- Require stimulation
- Quick
- Ipsilateral reflex
- Contralateral reflex
Monosynaptic (stretch reflex) one synapse
Polysynaptic
Withdrawal/ reciprocal inhibition reflex
Crossed extensor
5 Anatomical parts to the pathway
1-sensory receptor
2-Sensory (afferent) neuron (nerve)
3-Integration center
4-Motor (efferent) neuron (nerve)
5-Effector (site that recieves command)
- *Knee-jerk:**
- monosynaptic
- ipsilateral
IX The Glossopharyngeal Nerves
- *SM**-Innervates structures of the tongue and pharynx; cell bodies in medulla oblongata
- *Sensory**- Receptors in taste buds and posterior 1/3 of tongue and mucosa. Cell bodies in ganglia.
- *VM-** Parotid salavary gland
XI The Accessory Nerves
From Medulla
SM only – innervates sternocleidomastoid and trapezius
XII The Hypoglossal Nerves
From Medulla
Only Somatic Motor (SM)
Runs inferior to the tongue
Innervates the tongue muscles
