Anatomy & Physiology Lecture Outline: Week #6

• The Central Nervous System -- Ch.13a

LSc 107 Anatomy and Physiology Spring 1999

Thibodeau Ch 13 pp. 374-396

The Central Nervous System

• Brain and spinal cord
• Enclosed in bone (cranium, vertebrae)
• Surrounded by a bag of fluid (the meninges, containing CSF)

  Meninges: line skull Fig. 13-2

  dura mater

  • falx cerebri between cerebral hemispheres
  • falx cerebelli between cerebellar hemispheres
  • tentorium between cerebelli cerebrum and cerebellum

  arachnoid mater

  pia mater

Cerebrospinal fluid: Shock absorber, cushion

• Nutrient medium, carries some O₂, CO₂, 150 ml, clear colorless pH 7
• Contains water, salt and other electrolytes, glucose, small amount of protein
• Formed in the ventricles within the cerebral hemispheres

Fig. 13-5 CSF circulates down through brainstem, out and around outside of brain and spinal cord, reabsorbed back into venous sinuses inside skull

The spinal cord

• extends from foramen magnum to L1
• See X section Fig. 13-7
• H shape of grey matter - unmyelinated fibers and cell bodies
• White outer layer of myelinated fibers
• 31 segments - each segment has a pair of spinal nerves attached (peripheral nerves)
  • dorsal are 'incoming' sensory nerve roots
  • ventral are 'outgoing' motor nerve roots

Functions of the spinal cord

• conducts traffic to and from the brain
• acts as an integrating center for reflexes (in grey matter of cord)

Tracts of spinal cord

White matter is arranged into functional bundles or tracts

4 important sensory tracts (ascending) Table 13-1

• lateral spinothalamic tracts - crude touch, pain, temperature
• anterior spinothalamic tracts - crude touch and pressure
• cuneate and gracilis tracts - fine touch and posture sense
• spinocerebellar tracts - position and movement relayed to cerebellum (not conscious)

4 important motor tracts (descending) Table 13-2

• lateral corticospinal tracts - voluntary movement
• anterior corticospinal tracts - uncrossed voluntary movement
• reticulospinal - modification of motor movement
• rubrospinal - posture and coordination

The Brain

3 lb weight

100 billion neurons, 10X as many neuroglial cells

Brain cells formed before birth and in the first few months of life

NO NEW CELLS CAN BE FORMED

Structures of the brain: in order from below upward – medulla oblongata – pons – midbrain – cerebellum – diencephalon (interbrain) – cerebrum

brainstem: medulla oblongata, pons, midbrain

hindbrain: sometimes used to refer to the medulla oblongata, pons, and cerebellum

diencephalon: thalamus, hypothalamus, optic chiasma, pineal body

forebrain: cerebrum and basal ganglia

Medulla

• about 1 inch long, closest to the spinal cord, just below pons
• 2 parallel bulges on the ventral surface - the pyramids
• cardiovascular center
• part of respiratory center
• vomiting center, coughing, sneezing and hiccuping centers
• ascending sensory tracts pass through
• descending motor tracts pass through (in the pyramids)

Pons

• about 1 inch long
• acts as a bridge between medulla and midbrain, between halves of the cerebellum
• ascending sensory tracts and descending motor tracts
• part of respiratory center

Midbrain

• conducts impulses between hindbrain and forebrain
• ascending sensory pathways and descending motor pathways
• superior colliculi - visual tracking- reflex center
• inferior colliculi - auditory tracking - reflex center
• substantia nigra and red nucleus - part of extrapyramidal system involved in muscular control
• centers for certain cranial nerve reflexes

Cerebellum

• 2 hemispheres
• grey cortices
• white fibrous tracts inside
• cerebellar peduncles (3 prs) are the connections with the rest of CNS
• functions - balance and coordination - modifies conscious movement, and organizes muscle activity for balance and posture
• sensory input, and input from motor cortex
• output to motor cortex
• damage to cerebellum results in loss of coordinated functioning of skeletal muscle, and loss of balance; acts below the level of consciousness

Thalamus

• in center of brain, below the lateral ventricles
• 2 hemispheres joined in the midline by intermediate mass
• relay station for almost all sensory information entering the brain on its way up to the cerebral cortex
• crude appreciation of pain
• connections with many other parts of the CNS - (cerebral cortex, hypothalamus, motor system, reticular activating system)

Hypothalamus

• between the thalamus and the pituitary
• regulator of ANS
• origin of hormones of pituitary gland
• appetite center
• thermostat
• osmoreceptors

Cerebral Hemispheres

• the conscious brain - "higher centers"
• 2 hemipsheres
• grey cortex - cell bodies
• white medulla - connecting tracts
• gyri are bulges, sulci are grooves
• lobes: frontal, parietal, occipital, temporal Fig. 13-16

Functions of the cerebral cortex Figs. 13-19 & 13-20

• precentral gyrus - primary motor area - where voluntary movement starts
• Broca's area - motor speech area
• premotor area - learned movement
• post central gyrus - primary sensory area - where sensation is felt
• Wernicke's area - sensory speech area
• transverse gyrus of temporal lobe - primary auditory area,and association area
• Posterior pole occipital lobe - visual cortex and association area
• integrative functions of the cortex (the adding together of all available information, and the production of some kind of response to it: the modification of the activity in one system by activity in others)

consciousness - needs functioning cerebral cortex, reticular activating system
language - needs connections between sensory and motor speech areas, and memory areas (temporal lobe)
memory - storage and retrieval of information - temporal also parietal and occipital

 

The Limbic system Fig. 13-22

• part of the cerebral hemisphere
• buried in the center of the brain, surrounding the corpus callosum and underneath the ventricles surrounds the thalamus
• concerned with primitive emotion - fear, anger, sexual feelings

The Basal Ganglia (Cerebral nuclei) Fig. 13-18

• buried in the cerebral hemispheres- lateral to thalamus
• together with red nucleus and substantia nigra of midbrain form extrapyramidal system
• concerned with refinement of voluntary (cortical) movement
• damage causes Parkinson's disease

 

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