Introduction to the Nervous System
Prof. Vajira WeerasingheProfessor of Physiology
Faculty of MedicineUniversity of Peradeniya
(This lecture is available at www.slideshare.net/vajira54)
Why study nervous system?
Neurological diseases are disabling and debilitating and very little treatment
is available
Migraine (severe headache)
Stroke or paralysis Parkinsonism
Alzheimer’s disease (Memory loss)
Muscle wasting
Why study nervous system?
Activities such as walking and running and various forms of exercise and sports require
proper functioning of the nervous system
Controlling system
Nervous system is the main controlling system of the body QuickElectrical
Endocrine system also controls body functions SlowChemical
Nerve impulses
• It controls other organs by sending electrical messages called nerve impulses
• It is also the main communication system (like the telecommunication system)
What does it do ?Functions of the nervous system
1. Receives sensory messages from the external environment
2. Organizes information and integrates it with already stored information
3. Uses integrated information to send out messages to muscles and glands, producing organized movement and secretions
4. Provides the basis for conscious experience
Functional Subdivisions
• Sensory functions feeling, eg. pain
• Motor functionsmovement, eg. walking
• Integrative functionseg. reflexes
• Autonomic functionscontrol of blood pressure
• Higher functionsmemory, learning
Anatomical Subdivisions• Central Nervous system
Brain and spinal cord
• Peripheral Nervous systemCranial Nerves & Peripheral Nerves
• Autonomic systemsympathetic & parasympathetic
Brain
• Brain contains the main controlling centres
• It is divided into several lobes by several grooves
Brain - Lobes
• Frontal lobe Located in the frontPerforms motor functions
• Parietal lobe Located laterallyPerforms main sensory
functions
Brain - Lobes
• Occipital lobe Located in the backPerforms visual functions
• Temporal lobe Located laterallyPerforms hearing functions
White matter and grey matter
• In the nervous system Cell bodies are collected as
grey matter
Nerve fibres are collected as white matter
• In the brain grey matter is located in the
peripheral cell layer
White matter consists of central nerve fibre tracts
White matter and grey matter
• With nerve fibre tracts each lobe is connected to different structures of the body
• Frontal lobe is connected to the muscles
• Parietal lobe is connected to the sensory organs of the skin
• Occipital lobe is connected to the eye
• Temporal lobe is connected to the ear
Spinal cord
• Nerve fibre tracts starting from the brain then continue as spinal cord
• Divided into following areasCervicalThoracicLumbarSacral
Spinal cord
• Functions
To transmit impulses to and from the brain to the periphery
To cause reflex action
To process information
Peripheral nervous system
• Cranial nervesThere are 12 cranial nerves which
connects brain & brainstem with different organs of the head and neck region
• Spinal nerves There are several pairs connecting
different segments of the spinal cord with peripheral organs
Cranial nerves I-Olfactory nerve - smell
II-Optic nerve - vision
III-Occulomotor nerve - eye movements
IV-Trochlear nerve - eye movements
V-Trigeminal nerve - mastication
VI-Abducens nerve - eye movements
VII-Facial nerve - facial expressions
VIII-Vestibulocochlear nerve - hearing, balance
IX-Glossopharyngeal nerve - taste
X-Vagus nerve - parasympathetic
XI- Spinal accessory nerve - neck muscles
XII-Hypoglossal nerve - tongue
• Spinal nervesCervical
Thoracic
Lumbar
Sacral
Brain stem
• This is important part of the nervous system that connects brain with the spinal cord
• Many cranial nerves arise from brain stem
• It also contain vital centresCardiac, respiratory functions,
consciousness
Brain stem
• It has three areas
Midbrain
Pons (or pons Varoli)
Medulla (or medulla oblongata)
Cerebellum
• This is hind brain
• This is connected to the brainstem
• Main function is motor coordination
• Abnormalities result in difficulty in walking called “ataxia”
Sensory functions
• Functions that make us feel the environment
• Nerve signals come from the sensory organ towards the CNSAfferent signals
• There are different types of sensory modalities human nervous system could feel
General and special sensations
• There are two main types of sensations
General sensations
Special sensations
General sensations
• Mechanical sensations TouchPressureVibrationsStretch
• Thermal sensations Hot, cold
• Chemical sensation
• Pain sensation
Somatic and visceral sensations
• Somatic sensations External stimuli sensed by the skin
eg. Feeling of hot environment
• Visceral sensations Internal sensations sensed by the
visceral afferent nerves eg. acidity in stomach
Special sensations• These are specialised sensations
• Vision
Hearing
Taste
Smell
Proprioception
• Joint and position sensation
• Muscles and tendons contain receptors which could feel Muscle lengthJoint anglePosition of bones and joint
• This is very important feedback information for movements of muscles
General plan of the sensory system
• Stimulus
• Receptor
• Nerve pathway
• Central connections
• Brain area
Receptor
Sensory modality
Sensory nerve
Central Connections
Ascending Sensory pathway
Sensory area in the brain
Touch stimulus
AFFERENT
thalamus
sensory cortex
internal capsule
1st order neuron
2nd order neuron
3rd order neuron
Skin receptor
Spinal Cord
Brain stem
Motor functions
• Movements are of two types
Voluntary movements Consciously controlled
movementsWell thought and planned
Involuntary movements Reflex action Control of postureBalance
Voluntary movements
• Planning starts from the brain (frontal lobe)
• Modified by various intermediate structuresBrainstem Cerebellum
• Executed by the brainstem and spinal cord (lower motor neuron)
• Finally contraction of muscles
Brain stem
motor cortex
internal capsule
Uppermotorneuron
Lowermotorneuron
Muscle contraction
Spinal Cord
Motor Nerve
Motor map in the brain
• In the frontal lobe different areas controlling different muscles of the body are distinctly organised
• eg. there is a hand area, thumb area, face area
Representation
•upside down•distorted
concept of homunculus
Map
Cerebellum
• This is very important for motor coordination eg. In walking many muscles
should contract and relax in smooth coordination
• Cerebellum receives proprioception
• Cerebellum is used as an error correction centre
What is a reflex?
• Response to a stimulus
• Stimulus -> Response
• Task:Write down 3 reflexes.
Reflexes
• Response to a stimulus
• This is an involuntary actioneg. Hot object touching the hand
will cause it to withdraw
• This is called withdrawal reflex
What is a reflex?
Stimulus
Effector organ
Response
Centralconnections
Efferent nerve
Afferent nerveReceptor
Central control
Reflexes
• Reflexes involve many systems of the body
• eg.Withdrawal reflex (pain and motor pathways)Pupillary reflex (eye)Salivatory reflex (salivary glands)Swallowing reflex (GIT)Micturition reflex (urinary system) Baroreceptor reflex (blood pressure control)Stretch reflex (main reflex in the motor system)
Autonomic functions
• Controls involuntary functions of the body
• Two main divisions SympatheticParasympathetic
Sympathetic system
• This is involved in fight or flight reaction
• What happens when somebody is excitedBlood pressure increasesHeart rate increasesRespiratory rate increasesIncreased sweating Pupillary dilatation GIT function suppressed
Parasympathetic system
• This is involved when somebody s resting
• Blood pressure decreases
• Heart rate decreases
• Respiratory rate decreases
• Decreased sweating
• Pupillary constriction
• GIT function increased
Higher functions
• Brain is involved in controlling higher functions
• Learning
• Memory
• Intelligence
• They are called cognitive functions
Each side controls opposite of the body
• Right side of the brain controls left side of the body
• There is a cross over of nerve pathways at the brain stem
Basic cell in the nervous system is is a neuron
Nerve signals are electrochemical impulses called “action potentials”