Copyright 2010, John Wiley & Sons, Inc. Chapter 13 The Central Nervous System.

Copyright 2010, John Wiley & Sons, Inc.

Chapter 13

The Central Nervous System


Chapter 13: The Central Nervous System

The Central Nervous System (CNS) is the major control center for the body

In about 3 pounds of tissue, the CNS has 100 billion neurons

The brain collects sensory information, evaluates it, and sends instructions to effectors to direct appropriate responses

The spinal cord serves two major roles Serves as a pathway for information to and from the brain It controls rapid reactions (reflexes) to specific stimuli


CNS Overview: The Main Parts of the CNS The CNS consists of

The brain Cerebrum Diencephelon Brainstem Cerebellum

The spinal cord


CNS Overview: The Main Parts of the CNS


CNS Overview: Protection of the CNS

The CNS is protected by Bone

Cranial bones protect the brain Vertebrae protect the spinal cord

Three meninges (layers of connective tissue surrounding the CNS)

Cerebrospinal fluid (CSF) - the CNS is cushioned by a thin layer of fluid


CNS Overview: Protection of the CNS


CNS Overview: The Meninges and the Brain

The meninges are three connective tissue layers that surround the brain and spinal cord Dura mater

Epidural space Dural sinuses

Arachnoid mater Subarachnoid space

Pia mater


CNS Overview: The Meninges and the Brain


CNS Overview: Meninges and the Spinal Cord

The meninges also surround the spinal cord, and the cranial and spinal meniniges form a single unified protective covering for the CNS.


CNS Overview: Meninges and the Spinal Cord


CNS Overview: Blood Flow to the Brain Blood supply to the brain is a crucial source of O2

and nutrients

The brain receives much greater blood supply than expected based on its size and mass

Blood flow to active areas of the brain increases during higher levels of metabolic activity

Interruptions in blood flow have very serious consequences (unconsciousness, stroke, death)


CNS Overview: Blood Flow to the Brain


CNS Overview: The Blood-Brain Barrier The blood-brain barrier (BBB) prevents pathogens and

harmful chemicals from entering the brain

The BBB consists of 3 components Tight junctions between capillary endothelial cells A thick basement membrane underlying the endothelium A layer of astrocytes that cover the capillaries

The BBB helps prevent polar chemicals from entering the brain (but small, nonpolar chemicals enter easily)

Damage to the BBB exposes the brain to changes in blood chemistry and to pathogens


CNS Overview: Cerebrospinal Fluid

Cerebrospinal fluid (CSF) is a nutrient-rich fluid that circulates within and around the CNS

CSF serves three key homeostatic functions in the CNS

Mechanical protection

Chemical protection

Circulation


CNS Overview: Cerebrospinal Fluid


CNS Overview: Production of CSF CSF is produced in each ventricle Ependymal cells control which chemicals pass into CSF


CNS Overview: Circulation Pattern of CSF


The Cerebrum: Introduction The cerebrum is by far the largest part of the brain All conscious activities of the brain occur in the

cerebrum - this involves massive amounts of neural processing


The Cerebrum: Introduction


The Cerebrum: Terminology


The Cerebrum: Terminology

Key structural terms

Cerebral cortex Gray and white matter Cerebral hemispheres

Gyrus Sulcus Sissure


The Cerebrum: Lobes of the Cerebrum■Each cerebral hemisphere has several regions known as lobes:

Frontal lobe Parietal lobe Occipital lobe Temporal lobe The insula (deep to temporal lobe)

■Major grooves in cerebral surface Central sulcus Lateral sulcus Parieto-occipital sulcus


The Cerebrum: Lobes of the Cerebrum


The Cerebrum: Cerebral White Matter■Most of the cerebral white matter consists of fiber tracts - major groups of axons connecting distant regions of cerebral neurons

Association tracts connect gyri in the same hemisphere Commissural tracts connect areas in opposite

hemispheres Corpus callosum

Projection tracts connect the cerebrum to other brain regions

Internal capsule


The Cerebrum: Cerebral White Matter


The Cerebrum: Basal Nuclei

■Deep within the cerebrum are areas of gray matter called basal nuclei

■Major basal nuclei include Globus pallidus Putamen Caudate nucleus

■Basal nuclei are involved in the coordination of motor output, learning and many other functions


The Cerebrum: Basal Nuclei


The Cerebrum: The Limbic System■This ring-like set of structures (aka the “emotional

brain”) lies along the border of the cerebrum and diencephelon

■The limbic system mediates behaviors and emotions Pleasure and pain Fear/rage Affection

■The limbic system also has a major role in memory


The Cerebrum: The Limbic System


Functional Areas of the Cerebral Cortex■Regions of the cerebral cortex specialize in different

types of information processing

Sensory areas receive and process sensory impulses

Motor areas initiate voluntary movements

Association areas perform integrative functions


Functional Areas of the Cerebral Cortex


Sensory Areas of the Cerebral Cortex■Major sensory regions of the cerebral cortex include

Primary somatosensory area

Primary visual area

Primary auditory area

Primary gustatory area

Primary olfactory area


Sensory Areas of the Cerebral Cortex


Motor Areas of the Cerebral Cortex■Major motor regions of the cerebral cortex include

Primary motor area

Broca’s area


Motor Areas of the Cerebral Cortex


Integrative Areas of the Cerebral Cortex■Major integrative regions of the cerebral cortex include

Somatosensory association area Prefrontal cortex Visual association area

Wernicke’s area Common integrative area Premotor area


Integrative Areas of the Cerebral Cortex


Hemispheric Lateralization of the Cerebral Cortex

■There is functional asymmetry between the two cerebral hemispheres

Sensory information passes to the opposite side on its way in

Signals to voluntary muscles pass to the opposite side on their way out

■Many integrative functions are localized in one of the hemispheres, leading to terms such as “left brain” and “right brain” functions


Hemispheric Lateralization of the Cerebral Cortex


Diencephelon

The diencephelon is a small but crucial brain region that sits below and is surrounded by the cerebrum


Diencephelon Thalamus: Relays almost all sensory input to the cerebral cortex. Contributes to motor functions by transmitting information from the cerebellum and basal ganglia to the primary motor area of the cerebral cortex. Also plays a role in the maintenance of consciousness.

Hypothalamus: Controls and integrates activities of the autonomic nervous system and pituitary gland. Regulates emotional and behavioral patterns. Controls body temperature and regulates eating and drinking behavior. Helps maintain the waking state and establishes patterns of sleep. Produces hormones.

Pineal gland: Secretes melatonin, sets the body’s biological clock.


Diencephelon: The Thalamus

The thalamus has paired masses of gray matter, organized into many nuclei, located on either side of the third ventricle

The thalamus is a major relay center for information entering and leaving the brain, as well as for information moving within the brain


Diencephelon: The Thalamus


Diencephelon: The Hypothalamus

The hypothalamus is a small but critical brain region

Specific nuclei are involved in the control of Production of hormones

Emotions and behavior

Eating and drinking

Body temperature

Circadian rhythms and consciousness


Diencephelon: The Hypothalamus


Diencephelon: The Pineal Gland

This small region of the diencephelon secretes the hormone melatonin, and is involved in regulation of circadian rhythms and sleep


Diencephelon: The Pineal Gland


Brainstem Brainstem fiber tracts connect the spinal cord, the

diencephelon, and the cerebellum to each other Brainstem nuclei control many critical autonomic body

functions


Brainstem Midbrain: Relays motor impulses from the cerebral cortex to the pons and sensory impulses from the spinal cord to the thalamus. Superior colliculi coordinate movements of the head, eyes, and trunk in response to visual stimuli, and the inferior colliculi coordinate movements of the head, eyes, and trunk in response to auditory stimuli. Contributes to control of movements.

Pons: Relays impulses between cerebral cortex and cerebellum and between the medulla and midbrain. Pneumotaxic and apneustic area, together with the medulla oblongata, help control breathing.

Medulla oblongata: Relays motor and sensory impulses between other parts of the brain and the spinal cord. Vital centers regulate heartbeat, breathing (together with pneumotaxic and apneustic area of pons), and blood vessel diameter. Other centers coordinate swallowing, vomiting, coughing, sneezing, and hiccuping.

Reticular formation: Helps maintain consciousness, causes awakening from sleep, filters repetitive sensory input, and contributes to regulation of muscle tone.


Brainstem: Midbrain

Major midbrain structures include the cerebral peducles, the corpora quadrigemina, and the cerebral aqueduct

The midbrain includes major fiber tracts, as well as nuclei involved in responses to visual and auditory stimuli


Brainstem: Midbrain


Brainstem: Pons Major pons fiber tracts connect the cerebral cortex to the cerebellum

The pneumotaxic and apneustic areas help regulate breathing


Brainstem: Pons


Brainstem - Medulla Oblongata

Large fiber tracts in the medulla connect the spinal cord to the brain

The medulla includes control centers for respiration, heart rate, blood pressure, and other functions (e.g., coughing, vomiting, etc.)


Brainstem - Medulla Oblongata


Brainstem: Reticular Formation

The reticular formation is a diffuse collection of small nuclei in the brainstem - they act together to help maintain consciousness, and to regulate muscle tone


Brainstem: Reticular Formation


The Cerebellum The cerebellum is 10% of brain mass but contains almost 50% of all brain neurons

The cerebellum is critical to coordinated movements, and provides constant feedback to motor areas


The Cerebellum

Compares intended movements with what is actually happening to smooth and coordinate complex, skilled movements. Regulates posture and balance. May have a role in cognition and language processing.


The Cerebellum: Internal Structures

■Major structures and regions of the cerebellum are

Cerebellar hemispheres

Vermis

Arbor vitae

Cerebellar peduncles

Vitae


The Cerebellum: Internal Structures


The Spinal Cord

The spinal cord is the pathway taken by information traveling between our brains and our bodies

The spinal cord includes interneurons mediating spinal reflexes, as well as the cell bodies of all somatic motor neurons


The Spinal Cord

Conducts sensory nerve impulses toward the brain and motor nerve impulses from the brain toward skeletal muscles and other effector tissues. Integrates spinal reflexes.


The Spinal Cord: Gross Anatomy

■ The spinal cord has several distinctive features

Cervical enlargement

Lumbar enlargement

Conus medullaris

Filum terminale


The Spinal Cord: Gross Anatomy


The Spinal Cord: Spinal Nerves

■The spinal cord gives rise to the spinal nerves

Anterior root

Posterior root

Posterior root ganglion

Spinal nerve

■The most inferior of the spinal nerves form the

Cauda equina


The Spinal Cord: Internal Structure ■The spinal gray matter has a distinctive pattern

Anterior gray horns Lateral gray horns Posterior gray horns Gray commissure Central canal

■The spinal white matter has 3 sets of columns Anterior columns Lateral columns Posterior columns


The Spinal Cord: Internal Structure


The Spinal Cord: Sensory and Motor Tracts ■The spinal cord has a number of well understood fiber tracts and columns, that are named according to their origins and destinations.


The Spinal Cord: Sensory and Motor Tracts


Somatic Sensory and Motor PathwaysInteractions Animations Somatic Sensory and Motor Pathways

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End of Chapter 13

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Copyright 2010, John Wiley & Sons, Inc. Chapter 13 The Central Nervous System.

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Transcript of Copyright 2010, John Wiley & Sons, Inc. Chapter 13 The Central Nervous System.