NROB60 – Chapter 7
- The human brain appears complicated because it is distorted as a result of the selective growth
of some parts within the confines of the skull.
Gross Organization of the Mammalian Nervous System:
- The nervous system of all mammals has 2 divisions:
o The central nervous system (CNS)
o The peripheral nervous system (PNS)
- Using a rat’s example:
o Anterior or rostral – the direction or anatomical reference, pointing towards the
o Posterior or caudal – the direction pointing toward the rat’s tail
o Doral – the direction pointing up
o Ventral – the direction pointing down
- The nervous system is divided into 2 equal halves:
o Bilateral symmetry - the right side of the brain and spinal cord is the mirror image
of the left side
o Midline – the invisible line running down the middle of the nervous system
Medial – structures close to the midline
Lateral – structures farther away from the midline
o Ipsilateral - 2 structures that are on the same side
o Contralateral – 2 structures that are on the opposite sides of the midline
- To view the internal structure of the brain, it is usually necessary to slice it up
o Section – a slice (to slice is to section)
- The standard approach to is to make cuts parallel to one of the 3 anatomical planes of
o Midsagittal plane – the plane of the section resulting from splitting the brain into
equal right and left halves
Sagittal plane – sections parallel to the midsagittal plane
o Horizontal plane – perpendicular to the sagittal plane and is parallel to the ground
Horizontal sections splits the brain into dorsal and ventral parts
o Coronal plane – perpendicular to the sagittal plane and to the ground
Coronal plane splits the brain into anterior and posterior parts
The Central Nervous System:
- The central nervous system consists of the parts of the nervous system that are
encased in bone:
o The brain and the spinal cord
- The brain lies entirely within the skull, there are 3 parts that are common to all mammals
o Brain stem The Cerebrum:
- The rostral-most and largest part of the brain
- It is split down the middle into 2 cerebral hemispheres, separated by the deep sagittal
o The right cerebral hemisphere – receives sensations from, and controls
movements of the left side of the body
o The left cerebral hemisphere – concerned with sensations and movements from
the right side of the body
- Lies behind the cerebrum and contains as many neurons as both cerebral hemispheres
- It is a movement control center that has extensive connections with the cerebrum and
the spinal cord
o In contrast to the cerebral hemispheres, the left side of the cerebellum is
concerned with movements of the left side of the body. (right side same thing)
The Brain Stem:
- Forms the stalk from which the cerebral hemispheres and the cerebellum sprout
- It is a complex nexus of fibers and cells that serves to relay information from the
cerebrum to the spinal cord and cerebellum, and vice versa.
- It is also the site where vital functions are regulated, such as breathing, consciousness
and the control of body temperature.
o Brian stem is the most important to life, damage to the brain stem means rapid
The Spinal Cord:
- It is encased in the bony vertebral column and is attached to the brain stem
- It is the major conduit of information from the skin, joints, and muscles of the body to the
brain and vice versa.
o A transection of the spinal cord results in anesthesia (lack of feeling) in the skin
and paralysis of the muscles in parts of the body caudal to the cut.
Paralysis in this case, means that they cannot be controlled by the brain
- The spinal cord communicates with the body via the spinal nerves, which are part of the
peripheral nervous system.
o Each spinal nerve attaches to the spinal cord by means of 2 branches
Dorsal root – contains axons bringing information into the spinal cord
Ventral root – contains axons carrying information away from the spinal
The Peripheral Nervous System:
- The PNS has 2 parts:
o Somatic PNS
o Visceral (Autonomtic) PNS
The Somatic PNS:
- All the spinal nerves that innervate the skin, joints, and muscles that are under voluntary
control are part of the somatic PNS. o The somatic motor axons, which command muscle contraction, derive from
motor neurons in the ventral spinal cord.
The cell bodies of the motor neurons lie within the CNS, but their axons
are mostly in the PNS.
o The somatic sensory axons, which innervate and collect information from the
skin, muscles, and joints, enter the spinal cord via the dorsal roots.
The cell bodies of these neurons lie outside the spinal cord in clusters
called dorsal root ganglia.
The Visceral PNS:
- Also called the involuntary, or autonomic nervous system, consists of the neurons that
innervate the internal organs, blood vessels and glands.
o Visceral sensory axons bring information about visceral function to the CNS
Such as the pressure and oxygen content of the blood in the arteries
o Visceral motor fibers command the contraction and relaxation of muscles
Forming the walls of the intestines and the blood vessels (smooth
muscles), the rate of cardiac muscle contraction, and the secretory
function of various glands.
Afferent and Efferent Axons:
- Afferent (carry to) and efferent (carry from) indicate whether the axons are transporting
information toward or away from a particular point
o Afferents – the somatic or visceral sensory axons bringing information into the
o Efferents – the axons that emerge from the CNS to innervate the muscles and