Neurophysiology II: Functional Anatomy of the Brain and Spinal Cord (CNS) Lecture Notes PDF

Neurophysiology II: Functional Anatomy of the Brain and Spinal Cord (CNS) ANSC 3080 G. Bedecarrats Learning Objectives Describe the primary structure of the brain and spinal cord Understand the structure/function of the central nervo...

Neurophysiology II: Functional Anatomy of the Brain and Spinal Cord (CNS) ANSC 3080 G. Bedecarrats Learning Objectives Describe the primary structure of the brain and spinal cord Understand the structure/function of the central nervous system Organization of the CNS Brain Cerebrum (Forebrain) Diencephalon (thalamus, hypothalamus) Cerebellum Mesencephalon, Pons, Medulla oblongata (brain stem) Spinal cord 1  Task of the CNS  Receives continuous flow of information  From outside and inside the body  Analyzes and interprets the information  Makes sense of the internal and external info  Sends commands to the body to:  Maintain function of vital systems and organs  Respond to external environment  What sequence of events would be required for a horse to jump a fence?  Although very complex, the brain can be organized by structural (anatomical) features and function Meninges and Cerebrospinal Fluid Meninges:  3 layers surrounding the brain and spinal cord  Outer meninx = dura mater (thick, tough)  Supports the brain  Inserted between cerebral hemispheres  Forms the venous sinus, collects most of the blood and cerebrospinal fluid from the brain  Middle meninx = arachnoid  Inner meninx = pia mater, tightly attached to the neural tissue  Between arachnoid and pia mater is the sub-arachnoid space (filled with cerebrospinal fluid) 2 Cerebrospinal fluid (CSF):  Formed by capillaries of specialized areas of the pia mater called choroid plexus  Circulates from the brain’s ventricles down to the central canal of the spinal cord  Diffuses from 4th ventricle to the subarachnoid space and circulates around the brain and the spinal cord  Drained into venous sinus before entering blood circulation  Roles:  Provides nutrients to the CNS  Protection (shock absorber)  Ionic concentration ideal for optimum neuronal function  Blood- CSF barrier: at choroid plexus, uptake of nutrients and drugs into CSF Blood-Brain Barrier  NO CELLS or PROTEINS, low amino acids, only liposoluble substances (such as gases) can diffuse 3  Cerebrum Cerebral cortex (grey matter)  Acquired late in evolution, most superficial layer  Responsible for the conscious experience of sensory input  Site of high nervous association  Marked by a high degree of educability  Primary cortical areas have been mapped (mainly in humans) (somesthetic) Based on anatomical structure Based on response to stimulation Areas without define reactions = association cortex Neocortex: most complex part of the cerebrum Rhinencephalon = olfactory brain Mesencephalon = processes visual info in birds (part of the midbrain) FYI 4  Representation of body parts in the somatosensory cortex Representation of body parts in the motor cortex Equivalent representation of body parts in the somatosensory cortex of the rabbit and cat White matter:  Beneath the cortex, composed of myelinated nerve fibers  Includes:  Association fibers between parts of the cortex  Commissural fibers between the two hemispheres  Projection fibers: connect cortex to other brain structures and spinal cord Basal nuclei:  Deep within the cerebrum (close to the thalamus)  Paired nuclei composed of large pools of neurons  Control complex semi-voluntary movements (walking, running)  Work in conjunction with the cortex and cerebellum  In birds, also control voluntary movements Cerebellum  Not involved in consciousness and sensation but…  Receives information from the inner ear (equilibrium), proprioceptive receptors (muscles, tendons and joints), and cortex (visual and motor)  Main role is to prevent distortion of intended movement  Receives info regarding the status of the body, intended movement, and makes adjustment for a smooth completion  Corrective signals are sent via the thalamus to the cortex and spinal nuclei commanding the muscles  Well developed in animals requiring precise adjustment for locomotion (air, ground, water) 5  Diencephalon  Also called inter brain = hypothalamus, thalamus, and epithalamus  Thalamus = relay station for sensory information, cerebellum and basal ganglia, and the cerebral cortex  Epithalamus = contains olfactory correlation center and the pineal gland  Hypothalamus:  Produces neuropeptides that control the anterior pituitary  Produces neurohormones released by the posterior pituitary  Principal regulator of autonomic nervous system; with the brain stem, it is the most important region for the control of homeostasis Brain Stem Includes nuclei that govern body function by reflexes Also contains large amount of white matter (conveyers) 6 Mesencephalon:  Visual reflex center: receives visual info, controls eye movement (for focus)  Auditory reflex center: turn head for noise  In birds, well developed to process visual info  Most mammals’ midbrain very small, covered by cortex Pons and Medulla Oblongata:  Contain center for postural reflexes (hopping, righting, placing)  Control respiratory movements  Medulla oblongata crucial for control of:  Heart activity  Blood pressure  Relative distribution of blood to organs Cranial Nerves  12 pairs  I (olfactory) and II (optic) are the only purely sensory nerves and remain in the brain  III – XII all exit from the brain stem and innervate structures of the head and neck; most are both sensory and motor (mixed)  Exception is X = Vagus nerve: most widely distributed nerve throughout the body (from neck to abdomen)  Parasympathetic fibers to visceral structures in the thorax and abdomen 7  FYI Spinal Cord  Cervical, thoracic, lumbar, sacral, and coccygeal regions  Number differs between species Species C T L S Co Horse 7 18 6 5 15-20 Ox 7 13 6 5 18-20 Sheep 7 13 6-7 4 16-18 Goat 7 13 7 4 12 Hog 7 14-15 6-7 4 20-23 Dog 7 13 7 3 20-23 Chicken 14 7 14 6 Human 7 12 5 5 4 8  Central canal Dorsal surface Dorsal horn Ventral horn White matter Contains myelinated (giving the white appearance) and unmyelinated nerve fibers (axons) Arranged in columns or “tracts” Grey matter Contains cell bodies and dendrites Shaped like a butterfly Dorsal horn = sensory Ventral horn = motor (skeletal muscles) and autonomic fibers Middle zone = association 9  From FOX Spinal nerves Entry/exit of neurons from spinal cord Formed by joined dorsal and ventral roots, which merge within spinal canal Number = number of the vertebra they originate from Emerge from intervertebral foramina Each spinal segment receives sensory information from a section of the skin (dermatomes) and sends information to muscles (myotomes) Predicts the effect of spinal cord injury 10 FYI 11