Chapter 49

Nervous Systems

The nervous system is a combination of electrical & chemical signals that enable nerve cells to communicate with each other.

3 overlapping functions:1. __________

conduction of signals (light, smell) from sensory receptors to integration centers

2. __________ process by which the information from the environmental stimulation of the sensory receptors is interpreted and associated with appropriate responses of the body

Integration is carried out in the Central Nervous System (CNS) (brain & spinal cord in vertebrates)

3. __________ conduction of signals from the integration center to effector cells that actually carry out the body’s

responses to stimuli

Signals are conducted by nerves.Sensory input and Motor output are carried out in the Peripheral Nervous

System (PNS)

Overview of a vertebrate nervous system

• The spinal cord conveys information from the brain to the PNS

• The __________ also produces reflexes independently of the brain

• A __________ is the body’s automatic response to a stimulus

Nervous system is composed of:

1. __________

(nerve cell) functional unit of the nervous system

transmits signals from one location in the body to another

__________– convey nerve impulses toward the cell body

__________– convey nerve impulses away from the cell body

2. __________

provide structure

protect, insulate and assist neurons

Figure 48.2  Structure of a vertebrate neuron

Nervous systems:

1. A nerve net is a series of interconnected nerve cells 2. Sea stars have a nerve net in each arm connected by radial

nerves to a central nerve ring

More complex animals have nerves (bundles that consist of the axons of multiple nerve cells)

Fig. 49-2a

(a) Hydra (cnidarian)

Nerve net

Nervering

Radialnerve

(b) Sea star (echinoderm)

3. Nerve Cord

thick bundle of nerves usually extending through the body from the brain

4. Cephalization is the clustering of sensory organs at the front end of the body (anterior)

• Relatively simple cephalized animals, such as flatworms, have a central nervous system (CNS)

Fig. 49-2b

(c) Planarian (flatworm)

Nervecords

Transversenerve

Brain

EyespotBrain

(d) Leech (annelid)

Segmentalganglia

Ventralnervecord

Fig. 49-2c

(e) Insect (arthropod)

Segmentalganglia

Ventralnerve cord

BrainAnteriornerve ring

Longitudinalnerve cords

(f) Chiton (mollusc)

Ganglia

Fig. 49-2d

(g) Squid (mollusc)

Ganglia

Brain

Brain

Spinalcord(dorsalnervecord)

Sensoryganglia

(h) Salamander (vertebrate)

Fig. 49-4Peripheral nervoussystem (PNS)

Cranialnerves

Brain

Central nervoussystem (CNS)

GangliaoutsideCNS

Spinalnerves

Spinal cord

The vertebrate brain is regionally specialized :

• All vertebrate brains develop from three embryonic regions: forebrain, midbrain, and hindbrain

1. Forebrain includes:• Cerebrum

contains the most sophisticated integrating centers• Diencephalon develops into three regions:

– epithalamus includes the pineal gland and generates cerebrospinal fluid from blood

– thalamus - main input center for sensory information and main output center for motor information

– hypothalamus regulates homeostasis and basic survival behaviors such as feeding, fighting, fleeing, and reproducing; circadian rhythms

2. Midbrain:• midbrain contains centers for receipt and integration

of sensory information

• brainstem - coordinates and conducts information between brain centers

3. Hindbrain includes:– The pons regulates breathing centers in the medulla

– The medulla oblongata contains centers that control several functions including breathing, cardiovascular activity, swallowing, vomiting, and digestion

• Cerebellum controls movement and balance

Fig. 49-9c

Pons (part of brainstem), cerebellum

Spinal cord

Cerebrum (includes cerebral cortex, white matter,basal nuclei)

Diencephalon (thalamus, hypothalamus, epithalamus)

Midbrain (part of brainstem)

Medulla oblongata (part of brainstem)

Pituitarygland

Cerebrum

Cerebellum

Central canal

Diencephalon:

Hypothalamus

Thalamus

Pineal gland(part of epithalamus)

Brainstem:

Midbrain

Pons

Medullaoblongata

(c) Adult