Biomedical Engineering Reference
In-Depth Information
Withdrawal reflexes are elicited primarily by stimuli for pain and heat great enough to be
painful and are also known as protective or escape reflexes. They allow the body to respond
quickly to dangerous situations without taking additional time to send signals to and from
the brain and to process the information.
The brain is a large, soft mass of nervous tissue and consists of the cerebrum, the dien-
cephalon, the mesencephalon (midbrain), and the brain stem and cerebellum. The cerebrum
(Figure 3.30a), which is divided into two hemispheres, is the largest and most obvious
portion of the brain and consists of many convoluted ridges (gyri), narrow grooves (sulci),
and deep fissures, which result in a total surface area of about 2.25 m
2
. The outer layer of
the cerebrum, the cerebral cortex, is composed of gray matter (neurons with unmyelinated
HYPOTHALAMUS
CORPUS CALLOSUM
CEREBRUM
THALAMUS
PINEAL
BODY
MIDBRAIN
CEREBELLUM
LATERAL
SULCUS
PONS
MEDULLA OBLONGATA
(a)
(b)
White matter
Gray matter
Posterior median sulcus
Central canal
Posterior rootlets
Posterior root
Posterior root ganglion
Anterior median fissure
Pia mater
Spinal nerve
Anterior root
Subarachnoid space
Arachnoid
Anterior rootlets
Dura mater
(c)
Anterior view
FIGURE 3.30
(a) The exterior surface of the brain. (b) A midsagittal section through the brain. (c) Structure of
the spinal cord.
