Neuroanatomy Exam 2

How do neurons communicate within a neuron?

electrical signals

How do neurons communicate between neurons?

chemical signals

Graded, local potentials

added up as ions enter the neuron and restricted to one place in the nueron

Propagated potentials

travel down the neuron’s axon (action potentials)

Polar heads of the phospholipid bilayer

hydrophilic which love fluid and point toward the intracellular and extracellular fluid

Non-polar tails of the phospholipid bilayer

hydrophobic which fears fluid and points away from the fluid

What are the 2 main functions of the lipid bilayer?

1. isolates the cytoplasm of the neuron from the extracellular fluid

2. it serves as a capacitor which stores charges

Voltage gated ion channels

gate opens/closes based on changes in electrical membrane potential (ex: sodium channels)

Ligand gated ion channels

gate opens/closes based on the binding of a neurotransmitter or hormone called a ligand (ex: postsynaptic receptors that bind specific neurotransmitters)

Thermally gated ion channels

gate opens/closes based on temperature of the neron

Mechanically gate ion channels

gate opens/closes based on movement (hair cells in inner ear)

Selectivity

ion channels ability to allow only certain ion through

Channelopathies

disease caused by defective ion channels

Resting membrane potential

collective difference in electrical potential between the inside of the a neuron and outside of a neuron

What is a neurons resting potential?

-65 mV

Temporal summation

the adding up of postsynaptic potentials generated in the same neuron at slightly different times

Spatial summation

the adding up of postsynaptic potentials generated at spatially separate sites on a neuron

What are the steps of an action potential?

1. neuronal membrane begins at resting membrane potential

2. local excitatory state

3. threshold

4. rising phase (rapid depolarization)

5. peak

6. falling phase (repolarization)

7. hyperpolarization

8. resting membrane potential

Saltatory conduction

myelinated axons have bare regions called nodes of ranvier that contain many voltage-gated sodium channels

What are the steps of conventional synaptic transmission?

1. neurotransmitter synthesis

2. neurotransmitters are concentrated and packaged in synaptic vesicles which are found in presynaptic element

3. neurotransmitters are released into synaptic cleft

4. neurotransmitters bind to ion channels in postsynaptic membrane

5. neurotransmitter action is terminated in several ways

Excitatory postsynaptic potential (EPSP)

depolarizing potential change

Inhibitory postsynaptic potential (IPSP)

hyperpolarizing potential change that inhibits generation of an action potential by postsynaptic cell

ACh

major role in PNS excitatory functions, involved in CNS in movement and attention

Dopamine

• affects motor activity, cognition and behavior

• associated with pleasure and reward

Endorphins

inhibit CNS neurons involved in perception of pain

GABA

major role in CNS inhibitory functions (low levels could lead to seizures)

Glutamate

• fast excitatory NT of the CNS

• elicits neural changes associated with learning and development

Norepinephrine

• used by ANS, thalamus and hypothalamus

• associated with attentive functions and the fight or flight response

Serotonin

associated with mood and pain perception

Substance P

involved in perception of pain when tissue is injured

Myasthenia Gravis

autoimmune disease in which body produces antibodies that bind with ion channels in motor end plates preventing ACh from binding to these receptors resulting in severe muscle weakness

Botox

causes widespread paralysis by inhibiting the release of ACh at the neuromuscular junction

Schizophrenia

altered levels of dopamine

Parkinson’s

dopamine deficiency

Cocaine and amphetamine use

affects norepinephrine and dopamine signaling by. blocking reuptake

Panic disorder

associated with high levels of norepinephrine

Depression and suicidal behavior

low levels of serotonin

Interoreceptors

monitor events within the body

Proprioceptors

respond to changes in position of body and its parts

Exteroreceptors

monitor events external to the body

Adequate stimulus

the type of stimulus to which sensory receptors are the most sensitive

Chemoreceptors

respond to chemicals

Photoreceptors

respond to light

Thermoreceptors

respond to temp

mechanoreceptors

respond to physical deformation

nociceptors

respond to pain (can be chemical, thermal, or mechanical)

Receptor potential

graded, local electrical response of a sensory receptor

Grade potentials

they are action potentials in a sensory receptor cell

What are the types of somatosensory receptors?

pacinian corpuscle, meissner corpuscle, ruffini ending, endings around hairs, merkel endings, free nerve ending

Receptive fields

particular locations on our bodies where application of an adequate stimulus causes a receptor to respond

Congenital insensitivity to pain (CIP)

children born without ability to perceive pain

Hyperalgesia/sensitizations

enhancement of the sensation of pain which results from tissue damage

Neuralgia

severe persistent pain in the distribution of a cranial or spinal nerve

Thalamic pain syndrome

lesions in the posterior thalamus may cause chronic pain

Referred pain

pain experienced in a different area from where the painful stimulus was induced

Muscle spindles

sensory receptors that detect stretch (muscle length) in striated muscles

Golgi tendon organs (GTO’s)

sensory receptors that detect muscle tension

What are the 3 components peripheral nerves are surrounded by?

epineurium, perineurium, and endoneurium

Epineurium

dense, loose connective layer enclosing each peripheral nerve; continuous with dura mater

Perineurium

lies within the epineurium; sheath of connective tissue continuous with arachnoid enclosing each bundle of nerve fibers

Endoneurium

loose, delicate connective tissue layer within the perineurium in which individual nerve fibers are enclosed

Spinal cord segment

a portion of the spinal cord (SC) giving rise to a spinal nerve on each side

Dorsal rootlets

enter SC in posterolateral sulcus on each side of the posterior surface of the SC

Dorsal root ganglion (DRG)

collection of cell bodies of sensory nerves entering SC

Ventral rootlets

exit SC from the anterolateral sulcus on each side of the anterior surface of the SC

Dermatome

area of skin innervated by a single spinal cord segment (DRG)

Myotome

grou of muscles innervated by a single SC segment

Cervical enlargement

gives rise to spinal nerves

Lumbar enlargement

gives rise to spinal nerves for LE

Conus medullaris

cone-shaped caudal end of SC located around vertebral level L1-L2

Lumbar cistern

enlarged subarachnoid space from end of SC at vertebral level L1-L2 to end of dural sheath at vertebral level S2 (filled with CSF + cauda equina)

Cauda equina

dorsal and ventral roots

Denticulate ligaments

lateral extensions of pia mater that span to arachnoid and then to dura and heal suspend + laterally anchor SC

Filum terminale

inferior extension of pia mater at conus medullaris that is anchored caudally to the coccyx

POsterior horn

receives sensory input from dorsal roots

Substantia gelatinosa (SG)

caps posterior horn and deals mostly with pain and temperature information

Body of posterior horn

deals mostly with somatic and visceral sensory information

Anterior horn

contains cell bodies of motor neurons that supply skeletal muscle (aka alpha motor neurons or lower motor neurons)

What happens if the lower motor neurons are damaged?

causes flaccid paralysis (muscle limp, can’t contract, and eventually atrophies)

Intermediate gray matter

lies between anterior and posterior so it contains features of both

Intermediolateral (IL cell column)

present in T2-T3 and contains sympathetic nervous system neurons in the pointy lateral horn

Sacral parasympathetic nucleus

intermediate gray matter of S2-S4, but no distinct lateral horn

What are the 3 main funiculi of the SC?

posterior funiculus, lateral funiculus, and anterior funiculus

Posterior funiculus

located between posterior median sulcus and posterior horn

Lateral funiculus

located between sites where dorsal and ventral roots emerge from the spinal cord

Anterior funiculus

located between site where ventral roots emerge from the SC and anterior median fissure

What are the 2 fiber tracts of the posterior funiculus

fasciculus gracilis and fasciculus cuneatus

Spinal reflex

discharge of an efferent motor neuron in response to afferent stimulation of sufficient intensity

What do all spinal reflexes involve at a minimum?

a sensory receptor, an afferent (sensory) neuron, a synapse, and an efferent (motor) neuron

Monosynaptic or myotatic reflex (knee jerk reflex)

muscle spindle notes stretch and sends an action potential to SC

Flexion (withdrawl) reflex

free nerve endings respond to noxious stimulus and send action potential to SC

What are the 3 general functions of the brainstem?

conduit functions, cranial nerve functions, and integrative functions

Conduit functions

contains ascending and descending tracts that connect SC and rest of brain

Cranial nerve functions

CNIII - XII project to or emerge from the brainstem and are the structures that perform spinal cord-like functions for the head as well as subserve the special senses

Integrative functions

examples include complex motor patterns, life sustaining activities and regulation of consciousness

Tectum

found in midbrain only and comprised of superior and inferior colliculi

Tegmentum

consists of reticular formation, CN nuclei and tracts, ascending pathways from SC and some descending pathways

What is the function of the propriospoinal tract?

shorter tract that interconnects spinal cord levels

Ascending tracts

carry sensory information to the CNS and involve a 3 neuron connection

What is the spinal cord location for the PCML?

posterior column