Transcript Document
THE NERVOUS SYSTEM Divisions of the nervous system • Afferent • Central Nervous System – Brain and spinal cord – Sensory information from receptors to CNS • Efferent • Peripheral Nervous System – Motor commands to muscles and glands – Somatic division – All neural tissue outside CNS • Voluntary control over skeletal muscle – Autonomic division • Involuntary regulation of smooth and cardiac muscle, glands Neuronal Organization: CNS • Two kinds of neural tissue found in both brain and spinal cord: • 1. Gray matter • 2. White matter Neuronal Organization: CNS 1. Gray matter = unmyelinated neurons + neuroglia -forms the outer layer of the cerebrum = neural or cerebral cortex -also forms nuclei deep in the brain = clusters of neuronal cell bodies in CNS -collections of nuclei can form a center (higher brain function) Neuronal Organization: CNS • 2. White matter = myelinated axons of neurons • cell bodies are found in the gray matter • axons are bundled together to form White matter tracts • conduct nerve impulses from gray region to gray region • Brain – three types of tracts (commisural, association, projection) • Spinal cord - two types: sensory and motor tracts (ascending and descending) Major Regions of the Brain Figure 15.1 Major Divisions of the Brain Cerebrum • Cerebrum = largest portion of the brain -left and right cerebral hemispheres divided by the longitudinal fissure -hemispheres connected by the corpus callosum – many gyri and sulci have specific names e.g. Central sulcus •between the frontal and parietal lobes -cerebral cortex is folded into ridges and grooves -grooves = sulci -sulci divide the cerebrum into lobes -ridges = gyri (gyrus) -specific gyri are for the processing of sensation, area of voluntary movement, speech, all thought processes -called motor and sensory areas Cerebrum -cerebrum contains three categories of white matter tracts: a. commissural – join areas between hemispheres e.g. corpus callosum, anterior & posterior commissures b. association – joins areas within a hemisphere c. projection – joins cerebrum to brain stem Gray Matter Nuclei: Basal Ganglia • • modifies motor commands that have originated from the cerebral cortex comprised of several nuclei including the: • 1. caudate nucleus: role in • • • posture and limb movement 2. putamen: precedes or anticipates body movements 3. globus pallidus: regulates muscle tone for movements 4. substantia nigra: role in eye movements – high concentration of dopanergic neurons Diencephalon • thalamus: 80% of the diencephalon • paired oval masses of gray matter organized into nuclei, interspersed with white matter • major relay station for most sensory impulses from the SC & brain stem • relays motor information from cerebellum into the cerebrum • relays nerve impulses to and from different areas of the cerebrum, the brain stem & cerebellum •hypothalamus Diencephalon 1. control of the ANS – role in regulating smooth & cardiac muscle contraction 2. hormone production – oxytocin and anti-diuretic hormone (ADH) 3. regulates emotional and behavioral patterns – rage, aggression, pain and pleasure + sexual arousal 4. regulates eating & drinking 5. controls body temp Diencephalon •epithalamus – consists of the pineal gland and habenular nuclei -pineal gland – part of the endocrine system -secretes the hormone melatonin -increased secretion in dark -promote sleepiness and helps set the circadian rhythms of the body (awake/sleep period) •subthalamus – works with the cerebrum and cerebellum to control body movements BRAIN STEM •comprised of three structures: – midbrain – pons – medulla oblongata Medulla Oblongata – inferior most part of the brain stem – made up of white matter tracts and gray matter nuclei – white matter - sensory/ascending and motor/descending tracts – nuclei regulate autonomic functions – nuclei are known as reflex centers for regulating heartbeat and BP (cardiovascular center), respiration (respiratory center), plus vomiting, coughing, sneezing, hiccupping and swallowing -associated with 5 pairs of cranial nerves VIII IX X XI XII Pons • “bridge” • connection from cerebrum to cerebellum – consists of multiple nuclei and tracts – nuclei control both somatic (voluntary) and visceral (involuntary) motor responses MIDBRAIN • relay station between the cerebrum and the spinal cord, and between the cerebrum and cerebellum – extends from the pons to the diencephalon – as cerebral peduncles • white matter motor tracts through the pons into the SC • white matter sensory tracts up into the thalamus cerebral peduncle pons medulla oblongata MIDBRAIN • Posterior portion = tectum -midbrain also connects the cerebrum to cerebellum via cerebellar peduncles -white matter tracts (motor & sensory) -Corpora quadrigemina = superior & inferior colliculi -reflex centers for eye movement, head and neck movement (protection), pupil size and eye tracking thalamus pineal gland corpora quadrigemina median eminence medulla oblongata cerebellar peduncle Cerebellum – divided into hemisphere with lobes - like the cerebrum • anterior and posterior lobes – has a superficial layer of gray matter called the cerebellar cortex - like the brain – deep to this gray matter are tracts of white matter and gray matter nuclei – like the cerebrum – evaluates and coordinates involuntary and voluntary motor activities initiated by the cerebrum and corrects problems by sending info back to the cerebrum – regulates posture & balance – uses sensory data and stored memories – “muscle memory” • called the emotional brain • involved in linking olfaction and memory to basic emotional behaviors • main components: The Limbic System cingulate gyrus hypothalmic nuclei – 1. limbic lobe: includes the anterior thalmic nuclei hippocampus (within the fornix parahippocampal gyrus), the cingulate gyrus, the insula and the dentate gyrus corpus callosum – 2. amygdala: integration center between the limbic system, cerebrum and various sensory systems – 3. olfactory bulbs – 4. mammillary bodies of the olfactory tract hypothalamus mamillary body amygdala – 5. fornix - tract of white matter that parahippocampal gyrus connects the hippocampus to the hippocampus hypothalamus • fibers end at the mammillary bodies – 6. hypothalmic nuclei – other areas Protection: The Cranial Meninges • Cranium is covered with protective membranes = meninges – Cranial meninges are continuous with spinal meninges – 3 layers: 1. outer, fibrous dura mater – comprised of an outer endosteal layer and and inner meningeal layer – large spaces for the circulation of blood can be found between these two layers = sinuses e.g. superior sagittal sinus 2. middle arachnoid mater – the dura mater forms sheets 3. inner, thin pia mater (falx) that separate the cerebrum into hemispheres and the cerebellum from the cerebrum Cranial Meninges – there are spaces between these membranes – A. subarachnoid space: between the arachnoid and pia maters » large veins run through the subarachnoid space - e.g. cerebral veins – B. subdural space: between the arachnoid and the dura mater » potential space in the cranial region – C. epidural space – between the dura mater and the vertebral canal in the spinal column » potential space in the cranial region Protection: CSF • brain contains fluid-filled chambers = Ventricles – 2 lateral ventricles, 1 third ventricle, 1 fourth ventricle – connects to the central canal which runs into the spinal canal – These chambers contain cerebrospinal fluid – made by specialized cells in the ventricles – choroid plexus (ependymal cells) Flow of CSF •CSF continually circulates - ventricles and central canal to subarachnoid space •CSF is gradually reabsorbed into the blood through fingerlike projections into the dural venous sinuses = arachnoid granulations (arachnoid villi) The blood supply to the brain • Arterial blood reaches brain via internal carotid and the vertebral arteries – both give rise to the Circle of Willis • made up of communicating arteries and cerebral arteries – the posterior communicating and cerebral unite to form the basilar artery – the basilar the formed from the union of the vertebral arteries • Venous blood leaves via internal jugular veins Spinal Cord • length in adults = 16 to 18 inches • 31 segments – each with a pair of spinal nerves • Cervical and lumbar enlargements – cervical = C4 to T1, nerves to and from upper limbs – lumbar = T9 to T12, nerves to and from lower limbs •Cervical •and lumbar enlargements Spinal Cord • Tapers to conus medullaris at lumbar area • fragments into a cauda equinae as it runs through the sacral canal – dorsal & ventral roots of lowest spinal nerves • filium terminale arises from the conus medullaris – extension of the pia mater that anchors the SC to the coccyx Histology of the Spinal Cord • Central gray matter – Contains cell bodies of neurons and glial cells + unmyelinated axons – Gray matter projections are horns • Peripheral white matter – Myelinated and unmyelinated axons – Organized as tracts or columns Histology of the Spinal Cord • Organization of Gray Matter • 1. Posterior gray horns – sensory neurons entering the cord • 2. Anterior gray horns – somatic motor neuronal cell bodies • 3. Lateral gray horns – visceral motor neuronal cell bodies • Gray commissures – axons of interneurons crossing cord • Organization of White matter • Anterior, lateral and posterior white columns – tracts of myelinated neuronal axons – ascending = sensory information – descending = motor information White matter tracts