introduction to neuroanatomy

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Fernando J. Peraldo, MD, MPH

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Page 1: Introduction to Neuroanatomy

Fernando J. Peraldo, MD, MPH

Page 2: Introduction to Neuroanatomy

The Nervous System

the major controlling, regulatory, and communicating system in the body.

the center of all mental activity including thought, learning, and memory.

Together with the endocrine system controls the functions of the body; responsible for regulating and maintaining homeostasis.

is made up of the brain, the spinal cord, and the (peripheral) nerves that transmit information into and out of the brain and spinal cord. 

Page 3: Introduction to Neuroanatomy

The Nervous System

Central Nervous System (CNS)brainspinal cord

• Peripheral Nervous Systemnerve fibersnerve ganglia

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THE HUMAN BRAIN

divided into two halves, or hemispheres, which are separated by a very deep crevice. 

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THE HUMAN BRAIN

The brain is made up of three major parts:  the cerebrum, the brainstem, and the cerebellum.

There is a large bundle of "nerves" that relays messages between the left and right hemispheres. 

brain = cerebrum + cerebellum + brainstem

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View of the right side of the brain from the midline

Page 8: Introduction to Neuroanatomy

THE HUMAN BRAIN

The brainstem a "stalk" connecting the brain and the spinal cord

 - responsible for many life-sustaining functions, including regulation of breathing, heart rate, and blood pressure

- have parts concerned with regulation of sleep-wakefulness cycles and with levels of alertness

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THE HUMAN BRAIN

The cerebellum

- concerned with regulating movements

- also plays an important role in procedural memory and classical conditioning

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THE HUMAN BRAIN

The cerebrum

- concerned with our ability to think, to plan, to process sensory information, and to move; responsible for those abilities that make us most uniquely human

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4 geographic regions, or lobes of cerebrum

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Function Description Location

Motor Control of voluntary movement The back edge of the frontal lobes

Somatosensory Bodily sensations, including heat, cold, pain, pressure, and body position

The front edge of the parietal lobes

Vision Ability to see Occipital lobe

Auditory Ability to hear Top part of the temporal lobe

Speech Production (Motor Speech)

Ability to produce speech sounds  "Broca's" area in the frontal lobe in the left hemisphere

Speech planning and comprehension ("sensory" speech)

Ability to plan and understand speech

"Wernicke's" area at the junction of the partiety, temporal, and occipital lobes in the left hemisphere

Biologically – based motives

Control of drives to satisfy basic biological needs, such as hunger and thirst

Hypothalamus, loacted at the bottom of the brainstem, near where the brainstem meets the cerebrum

Limbic functions Regulation of emotions "Limbic system" consisting of a group of brain areas located near the corpus callosum and extending into the temporal lobes

Summary of localization of function in the brain

Page 13: Introduction to Neuroanatomy

                                                                                   

localization of functions in the left hemisphere of the cerebrum

Page 14: Introduction to Neuroanatomy

The Spinal Cord

connected to the brain, descends down the middle of the back and is surrounded and protected by the bony vertebral column

surrounded by a clear fluid called Cerebral Spinal Fluid (CSF), that acts as a cushion to protect the delicate nerve tissues against damage from banging against the inside of the vertebrae

consists of millions of nerve fibers which transmit electrical information to and from the limbs, trunk and organs of the body, back to and from the brain

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1 Spinal Nerve 2 Dorsal Root Ganglion3 Dorsal Root (Sensory)4 Ventral Root (Motor) 5 Central Canal 6 Grey Matter 7 White Matter

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The Spinal Cord:Ascending and Descending Spinal Tracts

Ascending tracts- within the spinal cord carry

sensory information from the body, upwards to the brain, such as touch, skin temperature, pain and joint position.

Descending tracts - within the spinal cord carry

information from the brain downwards to initiate movement and

control body functions.

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Spinal Nerves

branch off the spinal cord and pass out through a hole in each of the vertebrae

carry information from the spinal cord to the rest of the body, and from the body back up to the brain.

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Spinal Nerves

4 main groups of spinal nerves- Cervical Nerves "C" : (nerves in

the neck) supply movement and feeling to the arms, neck and upper trunk. Also control breathing.

- Thoracic Nerves "T" : (nerves in the upper back) supply the trunk and abdomen.

- Lumbar Nerves "L" and Sacral Nerves "S" : (nerves in the lower back) supply the legs, the bladder, bowel and sexual organs.

Page 19: Introduction to Neuroanatomy

Spinal Cord Nerve Levels

The level of the spinal cord segments do not relate exactly to the level of the vertebral bodies i.e. damage to the bone at a particular level e.g. L5 vertebrae does not necessarily mean damage to the spinal cord at the same spinal nerve level.

Page 20: Introduction to Neuroanatomy

Peripheral Nervous system

located outside the CNS contains nerves that extend throughout the

body Two parts to the PNS

1. Somatic nervous system - neurons deal with voluntary actions, Ex. run, play, swing, hit 2. Autonomic nervous system - generally deal with involuntary acts

Page 21: Introduction to Neuroanatomy

The Autonomic Nervous System

a part of the nervous system that is concerned with regulating internal bodily functions that are generally considered to be involuntary or automatic, such as digestion, heart rate, blood pressure, glandular secretions, and tear production.

made up of two parts with opposite functions:  1. sympathetic nervous system

2. parasympathetic nervous system.

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The Autonomic Nervous System

sympathetic nervous system- the "fight or flight" system.  It prepares the body for action- active when we are anxious or otherwise emotionally aroused

  - activity increases heart rate and blood pressure.

parasympathetic nervous system

- referred to as the "vegetative" system

- nurtures and rebuilds the body

- active during relaxation and rest

- Activity decreases heart rate and blood pressure and promotes digestion

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ORGANIZATION OF THE NERVOUS SYSTEM

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- are the basic structural and functional units of the nervous system- conducting nerve impulses- highly specialized and amitotic - generally large nerve cells

Neurons

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Neurons

- generated before birth- responsible for the reception, transmission, and processing of stimuli; triggering of certain cell activities; and release of neurotransmitters

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Neurons

3 parts of a neuron: - dendrites- cell body/

perikaryon- axon

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Neurons

Cell Body- the metabolic center of a neuron and contains the nucleus with at least one nucleolus and contains many of the typical cytoplasmic organelles but lacks centrioles

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Neurons

Dendrites - are cytoplasmic extensions, or processes, that project from the cell body- usually, but not always, short and branching, which increases their surface area to receive signals from other neurons - are called afferent processes because they transmit impulses to the neuron cell body.

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Neurons

Axons- also cytoplasmic extensions, or processes,

- there is only one axon that projects from each cell body- usually elongated, carries impulses away from the cell body (efferent process)- the "transmitting" process of the neurone

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Axons - may have infrequent branches called axon collaterals- Axons and axon collaterals terminate in many short branches or telodendria

distal ends of the telodendria are slightly enlarged to form synaptic bulbs

surrounded by a segmented, white, fatty substance called myelin or the myelin sheath.

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SYNAPSES

morphologically specialised contacts between a bouton formed by one neuron,the presynaptic

neuron,and the cell surface of another neuron, the postsynaptic

neuron

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SYNAPSES

Convert electrical signal from presynaptic cell into a chemical signal in the post synaptic cell

Transmit information by releasing chemical messengers (neurotransmitters/neuromodulators)

Formed by an axon terminal that delivers the signal and a region on the surface of another cell where a new signal is generated and a thin intercellular space called synaptic cleft

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Types of Neurons

According to size and shape of their processesMultipolar – more than 2 cell processes

one axon, multiple dendrites

Bipolar – one dendrite and one axonPseudounipolar – single process close to the

perikaryon and divides into 2 branches, one extending

to the peripheral ending, the other toward the CNS

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According to their functional roleMotor (efferent) neurons – control

effector organs such as muscle fibers, exocrine, and endocrine glands

Sensory (afferent) neurons – reception of

sensory stimuli from the environment and

from within the bodyInterneurons - or association neurons,

are located entirely within the CNS in which

they form the connecting link between the afferent and efferent neurons.

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SUPPORT CELLS OF THE NERVOUS TISSUE

Schwann cells- Support cells in peripheral nerves- form the myelin around myelinated peripheral axons.  - also envelop unmyelinated axons, but without the dense membrane wrapping which characterizes myelin.

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SUPPORT CELLS OF THE NERVOUS TISSUE

• satellite cells- support cells in peripheral ganglia - cells immediately surrounding the ganglion cells as one flattened layer

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SUPPORT CELLS OF THE NERVOUS TISSUE

Glial cells- most numerous cells within the central nervous system

-10 times more abundant in mammalian brain than neurons

- surround both cell bodies and their axonal and dendrite processes

- non-neuronal, supporting cells, neuroglia.

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SUPPORT CELLS OF THE NERVOUS TISSUE

Glial cells Astrocytes (or astroglia)

- may be involved in the removal of transmitters from synapses and the metabolism of transmitters. - the scar-forming cells of the CNS.

- participate in the maintenance of the composition of the

extracellular fluid.

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SUPPORT CELLS OF THE NERVOUS TISSUE

Glial cells Microglia

- small elongated cell with short irregular processes- phagocytic cells that representthe mononuclear phagocytic

system in nerve tissue- involved in inflammation and

repair in the adult CNS and release neutral proteases

and oxidative radicals

- mesodermal origin, derived from the cell line which also gives rise to monocytes, i.e. macrophage precursors

which circulate in the blood stream

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SUPPORT CELLS OF THE NERVOUS TISSUE

Oligodendroglia - form myelin sheath around axons in the CNS - the functional homologue of peripheral Schwann

cells.- have fewer and shorter processes. - in contrast to Schwann cells in the periphery,

form parts of the myelin sheath around several

axons.- responsible for normal propagation of action potentials

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SUPPORT CELLS OF THE NERVOUS TISSUE

ependymal cells - low columnar epithelial cells lining the ventricles of the brain and central canal of the spinal cord- often cilated, lack tight junctions which allows a free

exchange between cerebrospinal fluid and nervous tissue- have long basal processes and form the ventricular lining over the few CNS regions in which the blood-brain barrier is incomplete. - form tight junctions and control the exchange of

substances between these regions and surrounding nervous tissue or cerebrospinal fluid.

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Review: Introduction to the Nervous System

The nervous system is the major controlling, regulatory, and communicating system in the body. It is the center of all mental activity including thought, learning, and memory.

The various activities of the nervous system can be grouped together as three general, overlapping functions: sensory, integrative, and motor.

Neurons are the nerve cells that transmit impulses. Supporting cells are neuroglia.

Page 47: Introduction to Neuroanatomy

Review: Introduction to the Nervous System

The three components of a neuron are a cell body or soma, one or more afferent processes called dendrites, and a single efferent process called an axon.

The central nervous system consists of the brain and spinal cord. Cranial nerves, spinal nerves, and ganglia make up the peripheral nervous system.

The afferent division of the peripheral nervous system carries impulses to the CNS; the efferent division carries impulses away from the CNS.

Page 48: Introduction to Neuroanatomy

Review: Introduction to the Nervous System

There are three layers of meninges around the brain and spinal cord. The outer layer is dura mater, the middle layer is arachnoid, and the innermost layer is pia mater.

The spinal cord functions as a conduction pathway and as a reflex center. Sensory impulses travel to the brain on ascending tracts in the cord. Motor impulses travel on descending tracts.

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End of lecture

Thank you