CNS_notes.doc WCR 2016

(See Marieb & Hoehn chapter 12)

These notes do not cover the following sections of Ch.12 in Marieb & Hoehn 10th ed.: Folding During Development (first part of 12.1); Higher Mental Functions (all of 12.7); Developmental Aspects of the CNS (no number). We skipped those in lecture, due to limited time, and those sections will not be on the test.

WCR 2016

Brain

Major regions

Cerebrum (cerebral hemispheres)

Cerebral cortex, fissures, gyri, sulci

Diencephalon

Thalamus, hypothalamus, epithalamus

Brain stem

Midbrain, pons, medulla

Cerebellum

Brain ventricles

Contain CSF, lined with ependymal cells

Connected to each other & to central canal of spinal cord

Protection

Meninges

Dura, arachnoid, pia

Subdural space, subarachnoid space

Cerebrospinal fluid

“Made” by ependymal cells in choroid plexus

Circulates slowly

Exits via arachnoid granulations into superior sagittal sinus (into venous blood)

Brainstem

Midbrain

Superior colliculi – visual reflexes

Inferior colliculi – auditory reflexes

Reticular activating system (activation of RAS increases alertness)

Cerebral peduncles: ascending & descending fiber bundles

Substantia nigra – regulates basal nuclei

Neurons here that use dopamine as their transmitter are lost in Parkinson’s disease

Red nucleus – subconscious upper limb motor control/regulation

Nuclei for some cranial nerves

Pons

Bridge between cerebellum & rest of brain; bridge between midbrain & medulla oblongata

Ascending & descending fiber tracts

Respiratory centers – influence medullary respiratory centers

Nuclei for some cranial nerves

Medulla oblongata

All communication via brain & spinal cord passes through medulla

Autonomic control centers: cardiovascular, respiratory, solitary nucleus

“Pyramids” on ventral (front) surface: fibers of corticospinal (descending, motor) pathway

Decussation of the pyramids

Nucleus gracilis, nucleus cuneatus

Part of posterior column pathway from peripheral receptors to cerebral cortex – see below

Nuclei for some cranial nerves

Cerebellum

Attached to rest of brain via the pons

Subconscious control of motor activities

Input it receives include: proprioceptive, tactile, balance, visual, auditory

Outputs

Regulates balance, equilibrium by outputs to centers controlling postural muscles

Conscious & subconscious motor regulation & fine-tuning

Folia

Gray matter: outer layer (cerebellar cortex) & deep nuclei

White matter: includes arbor vitae

Diencephalon

Epithalamus

Pineal gland – secretes melatonin – regulates sleep/wake cycle

Thalamus: gateway to the cerebral cortex

Relay station for sensory information ascending to cerebral cortex

Spinothalamic & posterior columns pathways synapse here

Lateral geniculate nucleus

Relays visual information received from optic tract to cerebral cortex & midbrain

Medial geniculate nucleus

Relays auditory information to cerebral cortex & midbrain

Hypothalamus

Regulation of various subconscious functions:

Body temperature, feeding & drinking, sleep/wake, blood pressure, secretion of hormones by pituitary gland

Pituitary gland (part of endocrine system) hangs underneath it

Limbic system

Functional system, anatomically spread out

Regulates emotional state

Helps with memory storage & retrieval (“writing to & reading from memory”)

Linkage between conscious thoughts & autonomic function

Parts include:

Hippocampus (memory)

Amygdala (=amygdaloid body; sympathetic nervous system control)

Cerebrum

Basal Nuclei

Regulate voluntary movement

Receive input from cerebral cortex about body position, motor plans

Sends outputs to subconscious motor control areas (red nucleus & other brainstem areas) and to motor cortex (via thalamus)

Cerebral Cortex

Landmarks & lobes

Frontal, parietal, occipital, temporal, insular lobes

Lateral sulcus, central sulcus, longitudinal fissure (mid-sagittal)

Post-central gyrus, pre-central gyrus

Functions: Know the cerebral cortical locations of the following:

Primary motor cortex, motor association area, motor speech area (=Broca’s area)

Primary somatosensory cortex, somatic sensory association area, general interpretive area (Wernicke’s area)

Primary visual cortex, visual association area

Pre-frontal cortex (personality, abstract intellectual functions, long-range planning…)

Gustatory & olfactory cortex (Vis A&P incorrectly lists these under “Motor Cortex” in section 13.10.1, p.446. These are sensory, not motor, functions.)

Left versus right

White matter

Association fibers, corpus callosum, anterior commissure

Spinal Cord

Basic Anatomy of Spinal Cord

Cord: gray matter, white matter (what causes the difference?)

Cervical & lumbar enlargements; cauda equina (begin where cord ends, at L1-L2 level)

Spinal nerve numbering:

Nerve number = number of the vertebra below it, for C1-C8 (nerve C8 above vertebra T1)

Nerve number = number of the vertebra above it, for T1-T12, L1-L5, S1-S5

Spinal nerve (sensory & motor), dorsal root (sensory fibers only), ventral root (motor fibers only), dorsal root ganglion (cell bodies of sensory afferents in dorsal root)

Meninges

Dura mater

Arachnoid mater

Pia mater

CSF – in the subarachnoid space

Subarachnoid space: under or inside the arachnoid mater

Epidural space: just outside the dura

Lumbar puncture: getting a sample of CSF by withdraw CSF from subarach space at L3-L4 level

White & gray matter in cord

Gray matter: many cell bodies of neurons

posterior (sensory)

lateral (visceral motor neurons)

anterior (somatic motor neurons) horns

Neurons in gray matter nuclei organized by type of information (motor or sensory, visceral or somatic) and within that, often by body region served

White matter: axons

Posterior white column

Lateral white column

Anterior white column

Anterior white commisure: fibers crossing R-L and L-R

Each column has multiple tracts

Each tract is either ascending or descending (i.e. sensory or motor, i.e. afferent or efferent)

Tracts are organized by body region served

Sensory & Motor Pathways (= Ascending & Descending Pathways = Afferent & Efferent Pathways)

Sensory

Two pathways lead from peripheral sensory receptors (touch, temperature, pain, …) to cerebral cortex: spinothalamic and posterior (or dorsal) column pathways. For each pathway, know: where cell bodies/axons of 1st, 2nd, 3rd order neurons are/travel; what sensations are carried.

Common features of both pathways

1st order neuron cell body in DRG

1st order neuron’s axon enters spinal cord via dorsal root

2nd order neuron’s axon crosses midline, terminates in thalamus (synapse onto target neuron)

3rd order neuron in thalamus

3rd order neuron’s axon goes to primary somatosensory cortex (sensory homunculus)

Spinothalamic pathway

Posterior (or dorsal) column pathway

Motor

Corticospinal pathway (part of the pyramidal system, so called because part of the pathway involves descending fibers which form the “pyramids” on the ventral surface of the medulla)

Voluntary (conscious) skeletal muscle control

Motor homunculus

Upper & lower motor neurons (where are they?)

(There are other motor pathways which we will skip.)

Levels of motor control

From “lowest to highest”: spinal cord to … to cerebral cortex

Cerebellum interacts via feedback with control at multiple levels

Brain areas active during preparation for & execution of movements