SENSORY RECEPTION AND PROCESSING

Sensation (ascending) pathways

Ascending = sensory info TO brain

  • vibration, light, touch

  • 3 nerves: spinal cord, middle (secondary sensory neuron), thalamus

  1. nerve receptors transmit sensory information to spinal cord

  2. signal moves to brain

  3. nerves in thalamus (Boston train hub; in the center) interact and transmit signal in brain

  4. another nerve transmits the sensory signal to the sensory cortex

Somatosensory to cerebrum

  • Posterior column-medial lemniscus PCML: interprets fine touch (discriminative), vibration, 3D form and shape (“stereognosis”),

  • Spinothalamic: interprets non-discriminate touch (leaning against a wall), temperature, nociception (pain)

Somatosensory to cerebellum

  • posterior spinocerebellar tract

  • cuneocerebellar tract

Pattern of Ascending Pathways

receptor » primary neuron (dorsal root ganglion)» secondary neuron (brain stem/spinal cord) » Decussation: signal crossing sides of brain » thalamus » cerebral cortex (info center)

  • signal starts at left, it goes to the right brain

  • signal starts at right, it goes to the left brain

    ^^ decussation

Sensory Homunculus

  • primary sensory cortex is in the post central gyrus

  • size coordinates with amount of sensation

    • bigger = more sensation

    • smaller = less sensation

  • each finger has input. if cut off the brain adjusts and covers missing area with more input to remaining digits

ghost pain: brain mixing signals up (for digits)

Motor (descending) pathway

  1. motor cortex transmits signal through brain to spinal cord

  2. signals transmitted to muscles

upper motor neurons project to lower motor neurons for muscle fiber innervation

pathways leading to the inferior spinal cord

  • corticospinal system: interprets complex voluntary behavior, fine motor control

  • vestibulospinal tract:

    • lateral: maintains posture while moving

    • medial: coordinates head and eye movement, stabilizes head

General pathway

upper motor neuron (cortex, brainstem)» decussation » lower motor neuron, spinal cord/brianstem muscle fibers

primary motor cortex: simple, localized movement execution, single muscle recruitment

premotor and supplementary motor: controls muscles to orient and prepare for bodily action

parallel systems: different cortical areas will affect the same muscles but exhibit different movement

same sensation pattern in the motor homunculus just like sensory homunculus

AUDITORY PATHWAYS

cochlear nuclei » superior olivary nuc» lateral lemniscus» inferior colliculus » medial genticulate »

changes sides on the body (“contralateral pathway”)

sound processed on both sides

TASTE

structures involved: geniculate ganglion, inferior ganglion of IX (vagus), inferior ganglion of X (glossopharyngeal) » solitary tract » solitary nucleus » central tegmental tract » VPM » internal brain capsule » gustatory cortex (insula) » orbitofrontal cortex or limbic system

does not change sides in the body (“ipsilateral pathway”)

OLFACTORY PATHWAYS (SMELL)

does not go to spinal cord or brainstem

[L nostril] receptors (nose nerves) » olfactory bulb » lateral olfactory tract » amygdala (memory) or primary olfactory cortex; [R nostril] anterior olfactory nucleus » anterior commissure » olfactory bulb in the right nostril

Projections to olfactory assoc. cortex and limbic structures

  • identify and separate odors

  • integration with taste cortex

  • learning

UMN V. LMN: Somatic Motor Pathways

upper motor neurons: cell body in CNS processing areas

lower motor neurons: cell body in a nucleus in the brainstem or spinal cord

importance: nerve damage, paralysis, kinesthetics can affect function

if UPM is affected by a lesion…

  • little wasting

  • increased tone

  • brisk reflexes (overdoing a reaction)

  • primitive reflexes (Babinski sign, reflexes that should have disappeared during development)

if LMN is affected by a lesion

  • wasting/atrophy from lack of signaling

  • normal or low tone (flaccidty)

  • reduced or absent reflexes

  • fasciculation (easy irritation of motor neuron)

FACIAL NERVE

  • right and left nucleus in facial motor nerves

  • contralateral

  • R motor cortex » signal to facial nerve » facial motor nucleus » signal goes to upper face or signal goes to L side » affects upper face and lower face ( also jumps to right side

Facial motor nucleus: mode of facial expression, posterior belly of digastric, stylohyloid m., stapedius m.

when UPM is cut, left lower face loses sensation

when LPM is cut, whole [left] side is affected

Chemical synapses have different specialized receptors

  • Biogenic Amine System: amine transmitters

    • enzymatically made by amino acids

    • Serotonin, dopamine, norepinephrine, epinephrine

  • Neuropeptide System: use molecules made from peptide-connected amino acids

    • Met-enkephalin, Substance P (short)]

    • Beta-endorphins, VIP (long)

Know all common neurotransmitters, their mechanisms, and their location and their comments

MAJOR ENDOCRINE SYSTEM ORGANS

Pituitary Gland: computer portion of brain (server with info on hormones)

Hypothalamus give input that stimulates hormone secretion