General Anatomy (Intro To Nervous Tissues) Flashcards
What is the Nervous system?
- A network of neurons
- To generate, modulate and transmit information between all the different parts of the human body
- Regulation of vital body functions (heartbeat, breathing, digestion), sensation and body movements
- Presiding over everything that makes us human: our consciousness, cognition, behaviour and memories
What is the central nervous system?
• Brain and spinal cord
• Vital organs – encased in bone for protection
• Integration and command center of the body
What is the peripheral nervous system?
• Peripheral nerves (cranial nerves, spinal nerves, and autonomic/ visceral nerves)
• Ganglia
• Functionally divided into somatic NS and autonomic NS (sympathetic, parasympathetic & enteric NSs)
• Conveying the information between CNS and the rest of the body
What is the brain and spinal cord?
➢ Brain
➢ Within the skull (forebrain, midbrain and hindbrain)
➢ Process the incoming information from peripheral tissues and generate commands
➢ Spinal cord
➢ It continues from the brainstem.
➢ Main function – to pass information between the CNS and periphery
➢ It also has the ability to generate commands but only for involuntary processes.
What is the PNS?
• 12 pairs of cranial nerves, 31 pairs of spinal nerves and ganglia (a number of small neuronal clusters throughout the body)
• Can be sensory (afferent), motor (efferent) or mixed (all spinal nerves are mixed)
- Somatic nervous system
• Sensory fibres from the skin, skeletal muscles and joints
• Motor fibres to the skeletal muscles (voluntary)
- Autonomic nervous system
• Involuntary motor control of organs and body functions
What is the sympathetic system?
• Adjusts our bodies for situations of
increased physical activity
• Commonly described as the “fightor-flight” response
• Faster breathing, increased heart
rate, elevated blood pressure, dilated
pupils and redirection of blood flow
from the skin, kidneys, stomach and intestines
to the heart and muscles
• Sympathetic fibers have a
thoracolumbar origin (from the T1-
L2/L3 spinal segments) & synapse
with prevertebral and paravertebral
ganglia, from which the postsynaptic
What is the parasympathetic
• Adjusts our bodies for energy
conservation (relax and reduce the
activities)
• For “rest and digest” or “feed and
breed” activities
• Slowing down the actions
of cardiovascular system, diverting
blood away from muscles and
increasing peristalsis and gland
secretion
• Craniosacral origin (from the
brainstem and S2-S4 spinal cord
segments)
• These fibers travel to thoracic and
abdominal organs, where they
What is white and gray matter?
➢ Myelinated axons – white (the sheath of axon/ myelin is white)
➢ Neuronal bodies and dendrites – gray
➢ Nervous tissue – divided into white matter (due to presence of axons) and gray matter (due to a large number of neurons present)
➢ Grey matter – cerebral cortex (outermost layer of the brain), and the central part of the spinal cord
➢ White matter – deeper tissues of the brain (subcortical) and the outermost layer of the spinal cord
What is the cross-section of the spinal cord?
• Gray matter core surrounded by white matter
• Gray matter – butterfly-shaped – on each side consisting of three columns: anterior, posterior and lateral horns
• Central canal – at the center of the spinal cord – filled with cerebrospinal fluid – running longitudinally through the entire length of the spinal cord
• The gray matter surrounding the central canal is composed of the anterior and
posterior gray commissures.
• White matter – space around the gray matter – consisting of fibres that ascend and
descend along the length of the cord. These fibres are divided into anatomical
columns: the anterior, posterior and lateral funiculi. Each funiculus contains a range of tracts.
What are the spinal nerves?
• 31 pairs
• Each pair is attached to a part of the spinal cord known as ‘spinal segment’.
• 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal
• Spinal nerve is formed by the ventral (motor) and dorsal (sensory) roots leaving and entering their respective ventral and dorsal horns. Each root consists of multiple rootlets.
• The dorsal root has a swelling called the dorsal root ganglion which houses the cell bodies of the sensory neurons.
• The ventral and dorsal roots join to form the spinal nerve proper, which passes a short distance through the intervertebral foramen before it branches into its ventral and dorsal rami. Rami have both sensory and motor fibres.
What are the branches of a typical spinal nerve?
• The ventral ramus is larger and forms the cervical, brachial and lumbosacral plexus and intercostal nerves supplying the arms, legs and anterolateral trunk. The dorsal ramus supplies the muscles and skin of the back.
• Dorsal ramus: curves backwards to supply the muscles and skin of the back
• Ventral ramus (called internal costal nerve in thoracic region): running just above the inferior border of the rib – to supply intercostal muscles
and skin on anterolateral aspect of trunk
What are the branches of ventral ramus?
• White and gray rami communicans: to connect the ventral ramus to sympathetic ganglion
• Muscular branches: to supply the intercostal muscles
• Branches to periosteum of ribs and parietal pleura
• Lateral cutaneous branch
• Anterior cutaneous branch
What is a Dermatome?
An area of the skin supplied by a spinal nerve
What is myotome?
• A group of muscles innervated by a single spinal nerve root.
• Myotomes are much more complex to test than
dermatomes, because each skeletal muscle is
innervated by nerves derived from more than one
spinal cord level, and are hence comprised of multiple myotomes
• E.g., Biceps Brachii muscle is innervated by the
musculocutaneous nerve, which is innervated by C5,
C6 and C7 nerve roots. All three of these spinal nerve
roots are said to be associated with elbow flexion.
What happens?
- C1/C2: neck
flexion/extension.
• C3: Lateral Neck Flexion.
• C4: shoulder elevation.
• C5: Shoulder abduction.
• C6: Elbow flexion/Wrist
Extension.
• C7: Elbow extension/Wrist
flexion.
• C8: Thumb extension.
