Chapter 7 The Brain

Regions of the Brain Cerebral hemispheres Diencephalon Brain stem Cerebellum  A good indication of intelligence is brain weight in relation to body weight.  Sperm whale = largest brain 20 lbs.   Mammal Body weight Brain weight How much of the animal is its brain? Blue whale 60 000 kg 6kg 0.01% Lion 200 kg 200g 0.1% Rat 200 g 3g 1.5% Human 70 kg 1.3 kg 1.9%    

1. Cerebral Hemispheres (Cerebrum) Paired (left and right) superior more than half of brain mass Gyrus, sulcus, lobes & fissure, gray VS white Figure 7.13a

Specialized Area of the Cerebrum Figure 7.13c

Layers of the Cerebrum White matter Fiber tracts inside the gray matter Example: corpus callosum connects hemispheres Basal nuclei – internal islands of gray matter Figure 7.13a

2. Diencephalon- Top of brain stem, in cerebrum 3 parts Epithalamus - has pineal body (an endocrine gland) & choroid plexus – makes cerebrospinal fluid Thalamus -Transfers impulses to correct part of the cortex localization and interpretation Hypothalamus - autonomic NS system center (regulates temp, water balance, metabolism), limbic sys (emotions); connects to pituitary gland.

3. Brain Stem - Attaches to the spinal cord Midbrain Reflex centers for vision & hearing Pons Mostly fiber tracts; nuclei involved in control of breathing Medulla oblongata Merges w/spinal cord; control centers for: Heart rate control Blood pressure regulation Breathing Swallowing Vomiting M P MO

4. Cerebellum 2 hemispheres with convoluted surfaces involuntary coordination of body movements

Protection of the CNS Scalp and skin Skull & vertebrae Meninges Cerebrospinal fluid Blood brain barrier

3. Meninges – connective tissue Dura mater - Double-layered external covering; folds inward -Periosteal – attached to surface of the skull -Meningeal layer – outer covering of the brain Arachnoid layer – Middle, web-like layer Pia mater - Internal layer, Clings to the surface of the brain

4. Cerebrospinal Fluid Similar to blood plasma Formed by choroid plexus watery cushion to protect the brain Circulated in arachnoid space, ventricles, & central canal of the spinal cord

5. Blood Brain Barrier Includes the least permeable capillaries Excludes many potentially harmful substances Useless against some substances Fats and fat soluble molecules Respiratory gases Alcohol Nicotine Anesthesia

Cranial Nerves 12 pairs of nerves that mostly serve the head and neck Numbered in order, front to back Most are mixed nerves, but three are sensory only

Spinal Cord Anatomy Exterior white matter – conduction tracts Internal gray matter - mostly cell bodies - Dorsal (posterior) horns - Anterior (ventral) horns Central canal filled w/ cerebrospinal fluid

Spinal Cord Anatomy Meninges cover spinal cord Nerves leave at each vertebrae Dorsal root Associated with the dorsal root ganglia – collections of cell bodies outside the central nervous system Ventral root

Spinal Nerves pair of nerves at each vertebrae - 31 pairs formed by combination of ventral & dorsal roots of the spinal cord nerves are named for the region from which they arise

Anatomy of Spinal Nerves Spinal nerves divide soon after leaving the spinal cord Dorsal rami – serve the skin and muscles of the posterior trunk Ventral rami – forms a complex of networks (plexus) for the anterior Figure 7.22b Slide 7.65 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Examples of Nerve Distribution Figure 7.23