CNS_notes.doc WCR 2015
(See Marieb & Hoehn chapter 12)
These notes do not cover the sections of chapter 12 on Higher Mental Functions, Homeostatic Imbalances of the
Brain, Diagnostic Procedures for Assessing CNS Dysfunction, or Developmental Aspects of the CNS. We
skipped those in lecture, due to limited time and those sections will not be on the test. – WCR 2015
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?)
(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